Where are you wanting to mount it and what type of retention are you wanting? I have a bladetech (I think that's the company) mag holster back home and the design for how it connects to my belt would allow one to mount it facing any of the 4 primary directions (mags can face up, down, towards your front, or towards your back). Basically the belt connector and the actual holster are two different things to allow for different mounting options. Biggest issue is that it is friction retention, so if it got loose then a mag could fall out.
Here is the link to what allows the holster to be attached at so many different angles. And personally I have the "glock" mag holster, but it holds my XDm mags just fine. As I said before though, it is only a retention holster so there's the possibility for them to fall out.