Theodosia. Echo in Florida has them for $4 per pack and they state it is one of their best sellers. I planted some two years ago and they bloomed early here in SE Texas Google Echo's nursery and book store and click on shop.
HTD

I highly recommend ECHO, they have several seeds that no one else has, and your money goes to a good cause. They are the best source, IMO, for Moringa oleifera.

That being said... winged bean is indeed a stretch for those of us in the North. I've tried ECHO's day-neutral winged beans, and even started early as transplants, they did not bloom until September. I only got a couple weeks of immature pods before frost.

Several other vendors have offered a day-neutral winged bean (including Nichols) but I can't help noticing that those who sell it are generally located in long-season areas. I'm not sure that there is presently a cultivar which will be anything but marginal in short Northern summers.

Hyacinth beans are also daylength sensitive, and after years of searching, I found a day-neutral cultivar last year... so there is cause to hope that a Northern-adapted winged bean might also be out there somewhere.

Thanks for your responses. Since my initial post, I did locate the seed at ECHO. Last year I did buy some from Nichols, but it did not seem to be any different in its sensitivity to day length than what I'd purchased elsewhere. I started them (the ones from Nichols) early in a greenhouse. I used a general legume inoculant, but I'm not sure if it did any good on this species. The vines started slowly, but too off my mid summer and were lush, covering their tall trellis and reaching into the nearby corn. However, by late October's frost, there was not even a sign of a bud, let alone a bloom or pod.

Echo also has day-neutral pigeon pea, which makes it possible to get a harvest in regions with 6 months or more frost-free and hot.