I had a custom holster made for mine. The RMR wasn't the sticking point for off-the-shelf holsters, the issue was the taller front "suppressor" sight.
As for OST... They just lowered their price on milling slides. You can send them your factory Glock slide and they will mill it for an RMR, supply plain suppressor sights and install said sights, then ship it back to you for under $150 total. You supply the RMR.
Or you can buy a complete slide from them already done.