Your best bet is to talk to your builder (engine), they may have a person that they could recommend. You can also start talking directly to the chassis/suspension builders and see what kinda deal you can strike yourself....youd be surprised this time of year.....if your ready to buy that is.
Tyson
LSR
MP Racing
Brooks
XTC
Tucker
to name a few. Besure to get actual specs (weight) on any arm that you buy....just cause it less, doesnt mean you wont pay somewhere else. Weigh out the difference in costs/weight of a round house vs. OEM style as well