There are plenty of coupons for national parks you can find online with search. The first one that I've found is the www.valpak.com. Upon entering their site, you will be presented an offer form. You can enter your zip code and email so that you will be alerted when coupons or offers are available in your area and you can choose which offers you'd like to subscribe to. There really are plenty you can find. Try these ones I’ve found for you and please take time to visit each site given here so you can get the details for the offers. Hope this helps.
http://www.valpak.com/coupons/search/YOSEMITE+NATIONAL+PARK/CA

ParkPartners.org is also a great site to find offers such as:
EVERGLADES NATIONAL PARK, FL -- SHARK VALLEY TRAM TOURS (TRF CONCESSION SPECIALISTS) - Shark Valley Tram Tours will be offering a "buy one, get one half off" price

GLACIER NATIONAL PARK, MT -- SWAN MOUNTAIN OUTFITTERS
Swan Mountain Outfitters will be offering the following discounts on the June 5-6, August 14-15 and September 25 in Glacier National Park:

1. Family Pack - $5 off standard rates for children ($17 and under) riding with a parent or guardian that pays full rate on any one or two hour ride

2. Group Pack - $5 off per rider for groups of 6 or more on any one or two hour ride

3. Montana Resident Pack - $5 off per rider for all Montana residents going on any one or two hour ride (proof of residency required)

LAKE MEAD NATIONAL RECREATION AREA, AZ - SEVEN CROWN RESORTS

Patio Boat Getaway Package
Stay two nights at Lake Mohave Resort on Lake Mohave in a spacious room with one king bed or two double beds
Enjoy one day patio boat rental
$250.00 plus tax and utilities. A $405.00 value!
Promotion Code: KPAT

Ski Boat Getaway Package
Stay two nights at Lake Mohave Resort on Lake Mohave in a spacious room with one king bed or two double beds
Enjoy one day ski boat rental
$275.00 plus tax and utilities. A $470.00 value!
Promotion code: KSKI

Promotional package is available April 16-21, 2010. Packages cannot be combined with any other discounts, specials or travel agent bookings. Additional nights available at regular rates.

Call (800) 752-9669 to check availability and to make your reservation. For more information, visit us at www.sevencrown.com/npweek.

There are more you can find when you visit here: http://www.parkpartners.org/Special-Offers-for-2010.html

See also these helpful sites:

Top Online Six Flags Coupons
http://www.the-bus.net/

Amusement Park Discount Coupons
http://themeparks.lovetoknow.com/Amusement_Park_Discount_Coupons

Mahalo has a helpful page for you, too! See http://www.mahalo.com/cliffs-amusement-park-coupon

Amusement Park Coupons + Printable Discount Tickets
http://www.refundsweepers.com/amusement-park-coupons.shtml

Popular Amusement Park Coupon Codes
http://www.retailmenot.com/coupons/amusementpark

Discount Coupons can save you a ton!
http://www.themeparkcodes.com/

Best Amusement Park Coupons
http://www.couponmountain.com/Amusement_Park-discounts-bargains.html

Hi @kerrryk! I found some coupons for amusement parks all over the U.S. You can try and take a look at the site.
Here are the coupons:

1.Coupon code: PepsiExcusive for SeaWorld.
Buy One Ticket Get One Free!!!!!! Ages 3 to adult)(that is 2 for $78.95)

2. Coupon code: MASON/OH for Kings Island
KINGS ISLAND/GREAT WOLF LODGE PACKAGE DEAL

3. Coupon code: cork2298 for Cedar Point Amusement Park
Up to $8.99 off admission

4. Coupon code: 401057052 for Lake Compounce
$6.00 off Regular Admission

5. Coupon code: 2010150 for Kenny Wood Amusement Park
15.00 discount on each ticket

6. Coupon code: WILD for Knott's Berry Farm
$26.99 adult tickets. valid till 3/31/11. "knotts" didn work for me but i found this one!

7. Coupon code: rummer for Splashtown
splashtown spring texas

8. Coupon code: 384 for Sea Breeze Amusement Park
$4.00 off for seabreeze from reliant credit union

9. Coupon code: Dm0008 for Splash Universe
$75 off bunkhouse suite

One can find coupons for amusement parks in many places for varying amounts.

Local grocery stores will sometimes have coupons and one can also find cans of soda, which have coupons printed on them. Of course using the can means that you have to cart the can with you to the amusement park, but there is also less of a chance of losing it!

Our local credit union also carries coupons for Six Flags Darien Lake, which is the closest theme park around here. Also various big businesses in town here namely Wal-Mart and Guthrie health care system give employees discount cards, which offer coupons.

The web sites of these major amusement parks will also have coupons as well as special deals, which are created to get more people on the property. SO try the web site and see where ya get.

Amusement park coupons are one of the most useful coupon when it comes to enjoying the fun rides available at an Amusement park. Using coupons can entitle you and your family savings on entrance fees to the park and it's featured rides. In order to maximize enjoyment in amusement parks, the best time for you to take advantage is during the non-peak periods for featured rides and attractions, they will probably offer rebates for family, groups and friends going to the park.

There are sites online wherein amusement park coupons is available, these are retailmenot.com, themeparkcodes.com, couponmountain.com, momsview.com, allacresstexas.com, refundsweepers.com, mousesavers.com]] and much much more.

The sites mentioned above will assist you in finding the most current amusement park coupons, which probably give you large discounts on family vacations. "Free online printable coupons, coupon codes, discount specials, deals and promo savings are readily available online at several of the coupon vendor sites across the internet."