I was googling mecgar mags for my P01 and it took me to a website called
www.ambientweather.com
I thought it was kind of weird, but I continued checking out their site because they had good prices on the mag I needed. They also carried other mags, and firearm accessories. On their main page you just see weather related stuff for sale, but if you search, or click on the "more manufacturers" link you can find mecgar, and many other names you'll recognize.
Anyways, has anyone else used this site? I received my mags promptly along with UPS tracking numbers. They seem to do good business so if they have what you want, go for it.