Where can I source Shelf Glide Racks?

Try Paul Flum. When I worked for Pepsi we got all of our racks from Paul Flum.

Display Technologies.

Both of those companies provide the majority of cold vault glides. Display Tech's are pretty nice if you like the clear plastic look (I prefer those).

PFI
http://www.pfinnovation.com/

or

Display Technologies
http://www.display-technologies.com/index.shtml

They're expensive, around $20 for each glide. Ouch!!

Display Industries
http://www.displayindustries.com

Thanks!