Firstly if you ring or e-mail JE Spares (might be worth asking for Ryan to all the guys know Kyosho stuff fairly well) with your requirements and I am 100% positive they will do everything they can to help you.
I believe that they order from Kyosho most weeks so if they haven't got it in the shop it shouldn't take much longer to get hold of it.
When I last chatted with Ryan he had just got back from a holiday and was about to get cracking on listing up the RB5 stuff but you know what it's like when you get back to work after a few weeks off I'm sure
I have a question for you though .. where are you finding a dirt track to race on????