At least 30 years old. Last used 1990s. REI has no idea what it is and can't find me the correct fuel to fit it. Any ideas? Brand, how do I adapt to use?

Looks like a Coleman Xponent Xpert. Probably a mantel piece.
Here's a pic on REI.com Discontinued long ago, it also uses a fuel bottle that is discontinued. Mods have been made by folks on this site (usually on the 2-burner) to allow use of isobutane canisters, but they still aren't necessarily useful/reliable in the field.

I'll let butthead chime in...

It used Coleman fuel. Grey can with red lettering. Was a very good burner. Folks at REI fawned over it. Shoulda just given it to them. Coleman brand makes sense. Thanks

Two burner, single burner, 3 legs, 4 legs. Coleman made a bunch, all with the same potmetal frame. All kind of frail. Now easily surpassed by new canister stoves.
What looks like a fuel line loop over the burner for pre-heating is a simple solid piece of brass round stock operating as a conductive heat sink.

butthead

butthead: "...Coleman made a bunch, all with the same potmetal frame..."

Xpert... Xtreme... Xpedition...
Coleman product naming team having a bit of fun.
Sort of fun to google them to see the subtle differences.