That'll be a nice trailie when restored mate!
The TSR125 was sold here from probably around 92/93 to about 1997.
In the evolution of the japanese 125 trail bike, they like the KDX125 were supposed to be slightly better and of a slightly newer design than the DT125R. I've known a few people say that the full power one's were a bit more lively than the DTR, but i bet there's not much in it tbh!
There's not many about now, and Suzuki didn't sell too many here, probably because they wern't too bothered about 2stroke 125's by then, and secondly because they stopped importing them, leaving just the DTR and KMX as the only bikes left.
I find it strange that your bike could be running a 125cc top end on a TSR200 bottom end. I would have thought that the stroke was different on the 200's? Having said that it might have either had a 125 crank fitted if the cases are the same, or it could have just been a much bigger bore on the 200's like the KMX's for example.
Anyway it would be nice to see a mint restored yellow/Blue RM styled replica made out of that, but with the TS graphics. I've got no idea on how easy they are to get parts for, but id start with the Suzuki Dealer's and see what's still available for them.
You do see a few 200cc versions on ebay from time to time, and it's possible a TS200R engine might show up at some point, but if they are anything like KMX engines they seem to be going for silly money now!

There's a KMX125 engine on ebay now listed at £450. No way in hell would i pay that for an engine id want to strip and re-build anyway.