Finding replacement baseboard metal components

I have some hydronic baseboard metal pieces in need of replacement due to not enough support brackets and kids climbing on them to look out the window, also i will need some support brackets.

There are no visible markings stamped on the pieces, what is the process to finding replacement components that will at least fit even if they don't match? I can post pictures if that would help but I would imagine someone out there has a cheat sheet with sketches of cross sections of major brands with measurements to at least know how to look in the used market.