Alex, some hobby stores will build it for you but for a price, of course. My suggestion for you is to just build it yourself. It's not that hard to build one. I personally haven't built an R40 but one thing for sure is that if you follow the directions, it shouldn't be that hard. ALSO, it will be easier for you to repair anything that needs fixing since you are already familiar with the car.I think the hardest part of building the kit is the differentials. Once you have that done, everything else will fall into place.
My first kit was the NTC3. Took me about 13 hours to build (divided over 3 evenings). It was my first kit, actually my first nitro. I took it as a learning experience and at least I can say that I built it.
Build it and run it till it breaks. It'll be easy to fix since you built it! Tuning it is different. That takes a little finesse and practice but that's what the board is for. Just ask.
Remember ... run, brek, fix ... run, break, fix ... it's an endless cycle.