[oblib]

I poked around a bit for US Gov data but didn't find much. Sure seems like they should have that somewhere.

I know the Old Farmers Almanac" has that data in their yearly booklet and on their website but not in a digital downloadable format.

You may have to key it in yourself but if you stick to just veggies it shouldn't be that much. You can adjust the planting dates to any zone once you have them for one zone according to the "last frost" date (AFAIK).