Correct me if I'm wrong, but can't we feed pumpkins to piggies at a rate of 1 pumpkin per seed? I swear that's how it used to work, but it's entirely possible that my addled brain is just failing me and making things up.
You can get seeds by feeding piggies, one pumpkin per pack. Problem is it's not worth feeding a 41c pumpkin to a piggy to get a 17c pack of seeds in return.
Plin, since it's a seasonal item all you have to do is keep the seeds around a while and then you'll be able to plant them in either a herb or crop garden during the in-game holiday Zilloween.
+1 I find this a cool nifty little idea, I would like the ability to get pumpkin seeds another way. Aswell with feeding pumpkins feeding to the pigs you very rarely get super harvests with pumpkins (im actually not sure if you do but they are rare) so you would be growing all your pumpkins just to turn them all back to seed, not worth it.