I used aluminum flat bar with rounded edges. This is the only supplier I could find that sells it with rounded edges. http://www.onlinemetals.com/merchant...p=2&top_cat=60
I use 1/4" and 3/8" wide. I rip it down the middle so I get two halves and file it smooth. The best way would be to bring it to a machine shop and have them machine it down to the height you want. Im always doing stuff the hard way to save me money, thats why I do it myself.
Or you can buy clayton machine works premade stuff. Just drill your mounting holes. For 1/4" I drill 3/32" and use #4 sheetmetal screws. For 3/8" I drill and tap, I cant remember the size I use. http://www.claytonmachine.com/interior-trim.html
Another option is to buy square bar and have a machine shop round the edges.