You
could do it yourself.
I drained my rusty tank, dropped it out, pulled the sending unit for cleaning, then ran water from a garden hose through the tank, (for a long time as I recall), to flush out the remaining gas and as much of the rust chunks as possible. I then had to use a flashlight for closer inspection, and a wire brush to break up more rusty spots, then flushed with water again.
I used a two-stage fuel tank resto kit from POR-15.
http://www.por15.com/
It took another day to cure, summer weather is best but, I used a heat lamp over the sending unit hole. Came out pretty nice. Coated the whole thing in a thick, grey, paint like substance.
Another option is to check with local radiator shops. Many of them do gas tanks, too.
~phiz