I bought virtually everything for mine from The Roadster Factory. Since it was a long-term project, I wasn't too concerned with the back-orders (and there were several). But whenever they had a sale on items I needed, I usually bought them then, as they typically had the best pricing during the sales. And they occasionally had some fantastic clearance deals.
Also, besides Charles, the owner, Dave and John were extremely helpful with technical expertise. They walked me through lots of sticky situations, and always seemed to be available. But it has been a while since I've bought anything from them.