I can't find a model number for the Chinese version online, so ask your in-laws to look at one in a store, pop off the back, pop out the battery and look on the label for the model number. Then search for that model number online. (You may not be able to buy it outside China, though.) And make sure it comes with a Chinese warranty. Having to ship it back to the US or UK (or wherever you bought it) for minor repairs wouldn't be too good.
(Actually, the best way to do it is for you to pay for it at a retailer close to them, so they can walk it back if there's a problem. Either find the retailer and contact them or send your in-laws an international money order or some other way that will work in China. Even buying them a Chinese credit card might work, if you give their address as the address of record for the card, so it's sent to them.)