Bill, I sold steel pipe in the 90's but no galvanized before that. I don't remember hearing of a problem and, really, your best source of info may be the grumpy old guy behind the counter of your local PVF distributor.
In any case, you may have a problem because there are only 2 domestic pipe manufacturers left, Wheatland and Sharon. Wheatland bought Sawhill a few years ago so you might have a case there. Other than that, any of the manufacturers that I can think of from that era are gone. One that I know of has reorganized through bankruptcy Chapter 11 three times since then. Welcome to the world of "free trade".
Good luck and let us know what you find. There should be stencils on the pipe. If you post the wording on the stencil, I'll try to decipher it for you.