No luck in any of my stores. The best I’ve found is 1/8” from HobbyLobby. No Lowe’s here and Home Depot doesn’t have it. None of the hardware stores have it, nor the hobby stores. I’ve done a pretty exhaustive search.
As an interesting side note, I measured up the FT wooden control horns and firewalls. The control horns are about .071in, which is a bit thicker than 1/16”, and the firewalls are about .1”, which is a bit thicker than 3/23”. Meanwhile, the HobbyLobby 1/8” ply is .11, which is a bit smaller than 1/8“. I tried it in the Tutor landing gear tab and it fit without modification, so that’s what I’m going to do. I would still be happy to buy a sheet of 3/32“ from FT if they would list it on their store though.