Where do I find stock steel oval tubing?
I have a bike that was a prototype bike made in China. There was a short run contracted by a bike company to see if they wanted to pursue the design. It did hold up pretty well considering it was a small folder and I weigh about 245#. It did start fracturing in one area around the seat clamp. I decided after repairing it once and having the same cracks reappear, to just salvage what I can and put together another bike. I'm thinking of using the back triangle of a 20" BMX bike, the original forks, folding stem and handle bars, wheels and hinges. Basically just need to nail down a rear triangle and section of tubing that would go from the triangle to the head tube. My questions are; where can I find steel oval tubing that is about 3-4 inches by about 2 inches? I'm thinking I'll be able to find the rear triangle in chrome-moly. Is there anything I have to consider if the welder is welding chrome-moly to steel tubing? By salvaging what I can from my old folder, I should be able to put together a fairly decent new bike. Plus I have the experience of what I liked and didn't like about the old one and can build from that.
I appreciate any help you could advice me on this.