Check with Snook21 on Aquabid or on here. He had some 12-16" ones not that long ago. There haven't been any brought in since this time last year to my knowledge. Plan on a massive tank with 3"'/month growth.
Proteus, catfish are among my favorite fish. I am in the planning stages of building a 1000 + gl tank and I want to have a couple of different amazing catfish in there and I thing the Firewood cats are beautiful.
sweet choice if got a massive tank, and have the resources for the upkeep sweet looking cats! i know theyre available at certain times of the year, certain species of fish have collecting seasons i do see them for sale from time to time
my best bet if youre dedicated waiting for the right specimens ask online sources thats known to deal with them or importers directly themselves when they usually send them out when theyre usually available
use all common trade names as well i just know john snookn21 is a great guy to work with ive brought alot of my catfish from him if want a referral that had those in the past ive not looked at his stocklist lately as im trying to get out of the hobby and not be tempted until after i move and is setttled in