Safariland and Blade tech do make HK45c holsters. When you posted about a serpa I was thinking along the lines of a duty or comp style holster. If it is going to be for concealment you may want to look into aquality leather unit. I carry my USP C 45 in a leather holster centerline/ appendix carry IWB. Centerline may not be for you, but I feel IWB holsters are easier to conceal. Look at Galco, Desantis, Milt Sparks. Their are a ton of good leather workers out there, but those should give you an idea. Go to a shop with a good selection and ask to try some holsters on. A good shop will let you do this.
George