Lou Alessi makes some very nice belt slides and OWB rigs for revolvers. He has an IWB rig similar to the Spark's Executive Companion too. Waiti times are in the 8-10 week range typically. Pricey, but excellent stuff.
My own preferwence above all others is Matt del Fatti. Expect wait times of up to a year because he is a true custom shop that will design anything you desire and only he works on all orders. I've never seen craftmanship better than his, Rosen included.