Does a high cap magazine exist for the USP Compact .45?  If so, where could I purchase one? Thanks.

No

Make one.  Take two 8 round mags, lop the top off of one and the floor plate ears off the other and have the bottom of the decapitated mag TIG welded on the bottom of the de-eared mag.  Clean up inside and out, refinish with Aluma-Hyde II matte black and use a STI 140 mm spring (Brownells, ~$8) and you have a 12 round Compact .45 mag.  A bit of work, sticks way out of the bottom of the pistol and is utterly worthless but it does function 100% and shows that anything can be done if you are stupid enough to do it.
The 12 round Compact .45 mag is the one on the right.


Two 8 round mags from CDNN: $40
Cutting and TIG welding:$20
Spring:$8
Total:$68
Kicks and Giggles: PRICELESS

WOW, I love the way you think!!!  Thanks for the replies.

Quoted: Make one.  Take two 8 round mags, lop the top off of one and the floor plate ears off the other and have the bottom of the decapitated mag TIG welded on the bottom of the de-eared mag.  Clean up inside and out, refinish with Aluma-Hyde II matte black and use a STI 140 mm spring (Brownells, ~$8) and you have a 12 round Compact .45 mag.  A bit of work, sticks way out of the bottom of the pistol and is utterly worthless but it does function 100% and shows that anything can be done if you are stupid enough to do it. The 12 round Compact .45 mag is the one on the right. img.photobucket.com/albums/v318/BiggBore/P1050007.jpg Two 8 round mags from CDNN: $40 Cutting and TIG welding:$20 Spring:$8 Total:$68 Kicks and Giggles: PRICELESS

Got a picture of the mag inserted?

How's this?  Not exactly "compact" any more is it?