To get you rolling, at a pinch, you might be able to use a CDI from, for example, a honda C50/70/90. There will be no advance, and you'll only be able to use one pulser coil (the one 12 degree one, green-white/green connection, otherwise kicking the bike will likely throw you over the handlebars) and you'll probably only be good up to about 3000rpm. If you do this, your top speed will be severely limited (80kph/50mph or so) and your motor will get hot at higher revs). It's not a perfect solution, indeed far from perfect, but it could dig you out of a nasty hole at a pinch.
Otherwise, you can use any Yamaha CDI (with a bit of fudging of connections) from the following models : 34L, 55W, 43F, 3AJ, 1VJ, 3UW, 59X, 3SW, 36A, 5Y1, 5Y3, 2KF, 2NF and kickstart models of 3TB. Curves will differ, especially for the 5Y3 CDI (XT550 model)
If you can't source an original CDI, and you're relatively handy with a soldering iron, try CDI pour XT600-XT550
. Cheaper than buying one from Yamaha, but you'll need to find someone with a PIC programmer (local robotics clubs, etc, you might be able to bung someone a bit of cash to make one up for you even)