This thread had discussion about cowpeas. Baker Creek was recommended as having many varieties.

Crowders and cowpeas are the same plant, aren't they? Vigna unguiculata?

Here is a link that might be useful: Baker Creek Cowpeas

They sound an awful lot like the zipper creams that I grow.

White pea, size the English pea Alaska, possibly White Acre. I am not aware of a White Crowder. Crowders are cowpeas which are crowded in the hull, resulting in flat ends on the seeds. Zipper is a cream pea that is greenish when cooked as a green shellie so it also a good possibilty.