Looking last night for levelers and found a couple additional sources.
Sunnex has a full line of nice stuff. Check the mounts section - about 6 different kinds.
http://www.sunnexonline.com/mounts
Also here:
www1.MSCDirect.com floor locks section
You could also do a home built deal with a 5/8's threaded rod through a sleeve tube , couple nuts, washers, and a rubber/nylon foot. Weld the lower nut to the bottom of the sleeve and maybe weld a cheap 3/8's or 1/2 inch socket to the top. Just a thought give this economy....
Jim