[Razor]

Well, there are several options to make this happen. First off, you can go the expensive route and get the Paraclete 'taco' holster, which provides a user-adjustable cant, but costs around $95 (you can probably get it for much less through GSA, though). The drawback of this (besides price and availability) is that with the holster mounted horizontally, there won't be as much secured Velcro between holster body and 'taco' attachment panel. Check out Lightfighter.com for a good picture of this holster.

Next, you could contact Gene at High Speed Gear and order his horizontal PALS holster. Its specifically made for horizontal carry (I've attached a pic, as I didn't see one on his website) and PALS attachment. Not sure on availability or price on this one. Downside is possible limited availability, and you're fixed at horizontal carry only.

Another option is the Tactical Tailor modular holster. Yes, I know its set up for vertical carry, but if you weave some MALICE clips through the vertical webbing on your vest or plate carrier, you can now mount the holster on the MALICE clips, making it horizontal. Drawbacks are extra bulk and weight due to the additional MALICE clips, and possible retention problems (not sure how well the pistol would ride in the holster as the retention strap is made for vertical security).

One other option would be to contact a custom gear maker, and have him sew up a PALS panel adapter that allows you to mount gear horizontally on vertically oriented PALS webbing. Then you could use any PALS compatible holster to solve your orientation issue. Drawbacks are the same as those for the TT jury rig idea above (extra bulk and retention). There are a few of us here that could do that for you pretty easily.

Hope that gives you some ideas.