Hi,
I have a Street Weapon sitting on my shelf at home with the same problem. I have the uprated green Losi front and side belts from the XX4 as these were all I could find. I did manage to get a few original rear belts but they crumbled into blue goo and string after a few races. I even tried boiling them before using them and soaking them in fabric conditioner, neither of which made any difference. I guess the belts were just not made for long term storage.
If anyone can get you an original belt it will be Darren from DMS-Racing in Watford. He often posts on here and is always really helpful.
I heard a story that belts from the HPI micro RS4 would fit and bought one to try. Unfortunately its a few teeth too long, and this makes all the difference. I think it might possibly work if you managed to put a belt tensioner into the belt tunnel but I was reluctant to start messing about drilling holes in the chassis.
Another alternative might be to find some other belt manufacturer that could make the right sized belt. Apparently they are 3MR pitch with 112 teeth.
http://www.rctech.net/forum/electric...rear-belt.html
If you have any luck with this then please let me know, as I would love to get my SW running again. In the meantime you could always run it as front wheel drive?
Ben