tonka2shoes - Yes you can use the Red Snappers with a 12" throat machine. They work with my 9" throat machine. You just have to pin the backing, batting and quilt top to the take-up roller (hopefully you have a Velcro applied leader on the take-up roller). Then you can use the Red Snappers for the bottom end of both the backing and quilt top.
kdeems - Here is the site to purchase them:
http://www.longarmsupplies.net/red_snappers.aspx