Electrical Mechanical Tubing. You can get it from your local hardware store for a reasonably inexpensive price, standard length is 10' I believe. The gate hangers are basically the big beefy hinges like ranchers use to build a livestock gate with, maybe some one that is better with posting pics could help out, a picture will make way more sense. If there is a little play in between the "spindle" and bearing, that's ok.
I used the heavier galvanized pipe from my local Ace Hardware, with wheelbarrow Bearings, and it has worked pretty well, I had them cut the pipe to length and ream out the inside of the pipe ends till the bearings just barely fit inside the pipe.
The homemade rollers do not quite as good, or sometimes better than, commercially available rollers, I've seen some nice ones, plus some pretty badly designed commercial rollers. These are way cheaper/work good.
We can't always agree, but we can still be civil to each other.