I got my long bolts from larkspeed. They were actually posted direct from a 3rd party, I think they were called grayston but can't 100% remember.
They're good quality, only thing I would mention is that they're normal bolt heads with a separate tapered part that you just drop on to the bolt before tightening onto the wheel. This is perfectly ok, just makes them a little more difficult to screw on as you can't put pressure on them with the socket. No problems with mine though, no wheels fallen off yet lol