The holster at the link below might work with a Ruger Redhawk with a red dot.
https://www.opticsplanet.com/galco-kodiak-hunter-shoulder-holster-for-s-w-n-fr-29-8-3-8-right-hand-havana-kh130h.html?_iv_parent-gun-model=ruger-redhawk&_iv_code=GC-HT8-GALH-KH130H&_iv_gun-model=ruger-blackhawk-dot-44-7-dot-5in,ruger-blackhawk-dot-357-7-dot-5in,ruger-blackhawk-7-dot-5in,ruger-redhawk-7-dot-5in,ruger-redhawk-7-dot-5in-w-scope,ruger-super-blackhawk-dot-44-7-dot-5in,ruger-super-blackhawk-7-dot-5in-w-scope,ruger-super-redhawk-7-dot-5in,ruger-super-redhawk-7-dot-5in-w-scope,smith-and-wesson-model-29-n-frame-revolver-8-dot-375in,smith-and-wesson-model-629-n-frame-revolver-8-dot-375in