Are sprockets pretty standard stuff...or will they be hard to find, like most other B4 parts?
The front sprocket, from the factory, has a rubber bushing on it,... it keeps things a little quieter. If you're not too concerned about that,.. a stock replacement sprocket can be ordered from nearly any aftermarket company that makes sprockets.
The rear sprocket is available aftermarket as well, and the chain is -definately- available aftermarket, just make sure you get the right size.
If the street bikes are anything like the dirtbikes, you usually buy the bike, and take the chain off, and replace it with aftermarket right away. So,.. don't worry about aftermarket at all.
The only reason I'm not sure about the quality of the chains on streetbikes, is that my 919 came with an aftermarket already on it, and Dita required a chain change, and one became available at exactly the right time. Thanks Pitter.
Perhaps if r_outsider comes back, he'll tell you more about my chains.