Omens are neat guns (anyone who knows me is familiar with my love of unconventional guns), but one thing that has bugged me about the design from day one is the breech screw - I hate having to haul out the hex wreches just to open up the breech for cleaning. So here's my solution - a knurled thumbscrew. Uses a stainless screw as the core so that there's no more rust and so that you can still use a hex wrench on it. The body is black anodized aluminum with a knurled surface. Also features a rubber washer to keep it from vibrating loose after finger tightening.
The Air Soldier Products Omen Breech Thumbscrew is newer, so it should be commonly available, both new and used.