Everbilt 1/2 in. x 1-1/2 in. x 36 in. Plain C-Channel with 1/8 in. Thick 800197 - The Home Depot
Outwater Outwater Alu565-M Mill Finish 7/8 Inch Inside Dimension Aluminum U Channel C Channel 72 Inch Lengths (Pack of 18 Pieces, 108 feet Total) at Lowes.com