hi,
yep go hpi site www.hpi.tv then find the parts you need then go on www.mirageracing.com/sarch.php then put in the part number u got from the hpi site (eg 458G8 made up lol) or just tipe in the sarch bar in the mirageracing site then put your car in, thats where i found out the price and if they make them now.
The Rs4 1,2, and racer all share probably 60% of what the rs4 3's have. With the exception of the drivetrain, most of it is the same, all the suspension parts, and where the suspension mounts to is all the same. The differentals are different, but internally they use the same parts. If you ever consider aftermarket parts, goto HPI's website and look at the RS4 3's manual and compare the part numbers to see if it's the same.
Also, feel free to contact any of the forum sponsors, they may not have the part in stock, but they'll most likely be able to order it.
I do agree with the parts being alittle harder to find.
At the time i got my NEW Nitro RS4 the parts were hanging on all the shelfs. Now I have to order everything.