Rails for sliding glass doors?

I have searched around and everyone keeps saying Lowe's or Home Depot but I have been to several stores and looked online and I can't seem to find what I am looking for, yet I look online (including here) and people seem to have them regularly.

Where in the world do you get the sliding frame rails for sliding glass doors? I am fine with them being adhesive but would rather they be able to be screwed. Perhaps I am just using the wrong terminology because when I go to the stores they keep taking me to large sliding glass doors and when I show them the glass I want to use they always tell me they don't have frames to fit it.

I am looking for rails that allow me to slide glass something like the image below


Thank you for all of the help.

Sorry double post Can a mod close/delete this one?

It looks like it will fit up to 1/4" if I read it right. They cut it to 6' sections.

http://ahturf.com/store/index.php?ro...oduct_id=69494

Maybe some stuff here too:

http://absupply.net/sliding-door-har...rack-sets.aspx

At the hardware store, it's generally called u-channel. It's not actually made for that purpose, but that's what most people use. On amazon they have the double u channel that is even better. For my custom cages, we made the track out of a wood strip that we used the table saw and cut channels down the strip.
Hope this helps.