Thanks for the lead, Gary. I called and unfortunately he knows of no source for a 62 Skylark tank new and I found nothing new for Buicks from 1954-64. He suggested custom fabrication with stainless steel, but didn't have a lead to someone who might do that. It would be an expensive, but permanent fix. I've found a couple at junkyards around the country (FL and OK), but they are rusty junk, not worth restoring. Still looking there - may be one in AZ which would motivate a visit to my sister there.
I might try to get someone to braze mine, replacing the putty that is leaking for a practical fix. Don't know what it looks like inside, but I suspect prior owner used ethanol gas and not driving it much, fuel dissociated with a water pocket on the bottom of the tank, causing it to rust inside. Metal is not soft in that area. I can get a guy here to run a camera inside to look at it further - might be my best option. Apparently, the poor seal job inside 2 years ago is now the biggest problem (fuel gauge didn't work because the float was stuck in the sealant). I've been told a caustic bath would never get all that old sealant out and it would flake off over time, clogging the fuel intake. I'm thinking a cleanup and brazing on the exterior only might be possible? Any thoughts, anyone?