Bridgestone 450, A Camera, 46x18 Fixed Gear, Homebrew Tandem
Not to bum you out or anything, but Free Spirits are old, extremely crappy bikes sold by Sears. I know this because a friend dumped one on me. The only part I could use was the drop bars which I cut and turned into bullhorns. - most everything else is nonstandard/hard to find. I think you'd have to look for BMX parts for most replacements.
If you really need a seatpost, I have one from my free spirit, but it's at my parent's house. I can see if they can find it.