Check out the Area 419 "Universal" Arca rail. You will drill your stock for t-nuts with a forstner bit, epoxy them in and attach. There are quite a few of similar products out there to do the same. 419 stuff is nice. HRD gear is local to Colorado and the owner is good people. They sell those at Mile High. They are some less expensive one too. I would skimp too much, you did just drop big cash on a RRS tripod, wouldn't want the rail to be the weak link.

If you need some other options PM me and I will look through my saved links and send them to you. If you only need a short piece of rail (4") and can wait a little, I have a buddy in Steamboat making some for a great price.