Backlit compatible, you may want to look at Ducky's sets, over at mechanicalkeyboards.com. With the Pure and those sets, you may not be able to fit the right shift key.
Other than those, you should be able to get any set that are sold in group buys so long as you also pick up a ISO set. You need the smaller right shift and extra key. You'll have to just accept the ISO enter key and such in the process.