There is very little professional level support in the USA for the Chinese bikes, however there is in other countries the UK seems to be doing more then anyone here and that could get you information and help you identify things your may need.
http://www.chinesemotorcyclepartsonl...o_PRING015.php
That is if you buy one and run into trouble with it then you can take it all apart and sell it online, E bay is a good place to do that, so any purchase of a used Chinese bikes is or could result in just a temporary online parts store. You can be sure that there are enough used GS250 in the USA and those that bought them are forced to be hunter gathers.