I have found that the best places to get parts are bikebandit.com, ebay.com, and bargainnews.com(Northeast I think). There are however, numerous other places, like junkyards, etc. Be aware that a lot of parts are interchangable among the TS and TC series motorcycles. But, also realize that these also cover a long time frame. For example, my bike has a cap that pops off completely, but earlier bikes had hinged caps. Also be aware that some items are year specific, for example my bike has a frame stamp of 11/78, that was the manufacture date, but it is a 1979 model.
I ran into a little problem with that discrepancy. On ebay, there was a seller selling a throttle cable for a 1979 TS185. I bought it as it was in good condition for a used part. However, when I recieved it, one of the ends did not fit my carburetor. I knew instantly it was from a bike that someone was parting out, looked at the frame stamp saw ?/79, and sold it as a 1979 model part, when in fact it was for a 1980!