Where are you in MD?

Depending on the FFL, some will take the hi-cap mag versions and for ~$10/ mag will limit them in various ways: some permanent (rivet, etc.) and some not so permanent (wooden dowel, etc.).

First you gotta find an online shop that will actually send guns with hi-cap mags to Maryland though...there are a few; just takes some due diligence. Some will send the mags with gun, no questions asked. Others will ship the gun, but no mags. Some will send the gun itself and for a couple bucks more send the mags to a friend, relative, etc. in a hi-cap mag friendly state instead. A few will refuse to ship the gun to MD at all.

Either that, or as already mentioned, you can try to find 10-round versions.

Also, what are you planning to do with it? Not that a G19 G5 is a bad gun or anything, but folks around here might be able to suggest a better option if you have a specific need in mind.