I have 7 of them, used , lightly used, great condition.16 bucks each, (2 to 5 dollar shiping depending on how many you buy)
free shipping if you take them all.
I'd also consider even trades for Ruger Mark II mags.
Best way to contact me is by email
I double checked the seven mags. 5 of them are Mark III mags The other two are just as new, but for the Mark II. When you remove the mag disconnect and install a hammer bushing, a common modification folks do to make the mags drop free, you can use either Mark II or III mags in your Mark III. I bought the two Mark II mags when the IIIs were out of stock. They cost the same new.