I have a couple of Randall left-handed 1911's, made in the mid 1980's they are the first "semi-custom" 1911's, they are also the first stainless and only high quality left handed 1911 ever made. I think total production of lefties is around 600 guns.  That being said, lets just say the aftermarket for left handed 1911 magazines is quite small.

I have one Service model that has been shot and has some wear and I wanted to shoot it a little more, I only have one mag.  I checked the usual places with no luck.  Any ideas on finding a good used or new spare mag?  They look like regular guns only backwards, mags are the same way.

why not get a gun smith to cut a notch on the other side of the mag body?
you may also need to have some work done to the follower.

I was going to do that myself if I cant find an extra original.