Yep, I'm here and maybe can help just a little. I'm just getting into copper enameling myself (still collecting supplies) and thought the same thing. Just found this by doing a search on the web. Looks easy enough actually. Scroll down and you'll see the trivets.
http://alohilanidesigns.com/making-trivets/ Not sure where to get the steel. I know Home Depot carries it but they are huge sheets.
Still, some of the trivets are pretty inexpensive. I think it's the shipping that gets ya if that's all one buys.
ETA: Here's another link to check.
https://billdawsonmetalsmith.com/how...clever-tricks/