Yeah, I hate those little parts. But how did you break the roll pin and not mess up all the aluminum? That's the real trick!
Unfortunately, that's not a standard part I have around (since I haven't managed to break one yet...:P)
You could try PT Firearms in Cross Plains WI. They seem to have parts when other people don't and usually have the small easy to lose parts laying about. They could probably just send you one in the mail as they are a little far away from you. The phone number is 608-798-0880
On another note, did you try the local hardware store? It is just a standard roll pin. You can always get one that's a little longer and cut it down before installing it.
I've lost a lot of front detent pins and a McGyver for that is a piece of a clothes hanger in case you ever need one.