I'm a new member of this site and just wanted to let you all know that I have a Magwell for the Ruger Mark III steel frame pistol available.
Here is a link to the website. The site is very basic as have just started it tonight!
It works very well, comes with the Magwell and six magazine extensions. It takes all of about ten minutes to install and only needs a 1/8th drill bit (and hand drill) to get it mounted.
Thanks for looking.