CSMC has several RBLs in stock and will/can mix and match them. They'll also do some customizing on existing guns.

As for weight, it varies considerably from gun to gun based upon wood density (typical). When I purchased my RBL 20 ga Lou let MD peruse the several RBL Reserves they had in stock so I could find the one I wanted weight wise. In English/splinter the weights varied from 5lb 8oz to almost 7 lbs. I settled on a 5 3/4lb gun with a bit of bbl heaviness. Once I added a pad to get me to 15 1/4" lop the gun balances just ahead of the pin and is a hair under 6lbs. Its a wonderfully light, but balanced, gun.