Ebay seems to be the best bet on tanks. I found one w/o dents and made an offer, which was accepted. Welder has it now, looking forward to a test fit next week. Going for ~8.5 Gal to match the wife's GSA range.
Used to be she had to add a couple of gallons to her fuel cell to match my stock tank range. Now it's the other way around!
I don't need 11 gallons too often any more, so will probably sell my original black '12 tank with the 4.8 gal flat bed fuel cell once the supertank is done and on the bike. Have to see if I like the Supertank or not once it's functional.