Seems like this question is slowly becoming more popular, usually online shops stock what you need, or big wholesalers like CMPO and eBay. However some things are just not readily available from these sources, such as valve heads, some particular engine big bore kits, EFI conversions and so on…
With China, the best place to source seems to be TaoBao, the Chinese equivalent of eBay. The problem is, communication, then many sellers won’t sell beyond china, due to not being able to sort out the delivery nor the tax at their end, this does create a problem. The good news is, you get companies that are agents and you tell them the item and they order it on your behalf, they take a very small merchant fee and money for the item. Order it to themselves, sort out shipping to you and invoice you for the final shipping costs. I use TaoBaoNow as my agents, they have been brilliant, if I asked for extra packaging they did, they even showed me pictures to double check everything in my EFI conversion kit was present, plus it still works out cheaper for many items to be obtained through China than many online stores and they do have a bigger variety.
The last problem with TaoBao is, sometimes its difficult to find what you are looking for, and translating tools don’t seem to word things correctly, so here’s a small list to some of the parts I have ordered to help you see what you are searching for and how things are phrased. Some sellers will also offer small extras in the description for a few Yuan more, ie better piston rings, ceramic coated piston etc.. So bare that in mind.
These parts may or may not be any longer available and are merely a reference, but you can try. My future upgrades yet to come are a 200/250 valve head and the EFI conversion followed by a new downpipe.
My XTR-S Project 