lubadub on this site can get you competition giant pumpkin seeds. He wrote a book on growing growing giant tomatoes as he grows both pumpkins and tomatoes. He grew one over 1000 pounds.

you can get them through the giant pumpkin groups around the country. this will get you the better seeds as they are carefully documented for genetics. they share the biggest of the big and the world largest seeds etc. not easy to get the super best seeds if you are slow. haha. the seeds from world champions are in demand.

the rare seeds from the very best are usually given to serious growers. but newbies at the hobby can get pretty close to the world champion seeds. The individual genetics in these seeds are very important if you are in competition to grow a really big pumpkin. try to link up with your local giant pumpkin growers group. use google and you should find them in a flash.