You may see a Thrux gel seat show up in the classifieds here or on ebay, but they are rare. They are rare for a reason: they are MUCH better than what you currently have. I'd advise biting the bullet and getting one, even if you have to pay retail. All the mods in the world won't be worth their weight if you can't stand to ride the bike.
"Cognito Ergo Wrenchum"