I'd search for heirloom corn via the search engines and you'll come up with lots of stuff. Talk to the folks at Lakeview Organic Grain in Penn Yan and they will be helpful. Even if your farm isn't certified organic you should do it all organic, forget about using roundup ready seed, no till corn and all that crap. I get a lot of my grain, and so far all my corn from Lakeview Organic. I know they've offered an heirloom corn in the past called Wapsie Valley and I understand that McKenzie Distilling near Watkins Glen uses that (or has).
As far as is known, distillers used both yellow corn and white corn. It probably was less sweet than what is available today but I don't know if distillers — and especially farm distillers — preferred of the old styles, whether they were roasting corn, creamer corn, field corn, or old fashioned kinds of "sweet" corn. Mike? John? any info on this, maybe ads in old distillers journals. It may be that for the old time distillers it didn't matter so much.
Again, I think most corn used for distilling these days is simply red grade corn. I use simply generic organic cracked corn and it seems to produce a nice whiskey. Feel free to contact me as I run a small distillery here in Walton, NY. Google Delaware Phoenix and you can get the number.
Cheryl Lins - Proprietor and distiller, Delaware Phoenix Distillery, Walton, NY