Furniture Grade Square PVC Pipe and Tube On Available Plastics, Inc.
3/4" OD x 0.060" Wall PVC Square Hollow Tube | U.S. Plastic Corp.
ABS Plastic Pipe ABS Tube Square Plastic Tube, Suitable for Making Models and Decorations, 500 Mm in Length,Side Length:4mm(30pcs) : Amazon.ca: Industrial & Scientific
How to convert PVC Pipe Square shape | Convert Round PVC Pipe into Square shape - YouTube