I recently bought a 73 TX125 and need some ideas where to find parts. I need a carburetor, rear seat shocks, and seat. Any ideas where I can starts or what after market parts I can use?

 

Craigslist and eBay. You can do a nationwide search on Craigslist to cover more are than where you live.
Also check out some indie shops to see what they have, they may be able to point you in a better local direction.