I always grew buckwheat as a cover crop in my garden (Big garden, one half in cover and the other half in crops, alternate each year). Very easy to grow. Remember, it's an annual. It does self seed to some degree if planted early enough in the season. If you have a feed store nearby they should be able to supply you with seed.I once was in a feed store and the owner told me he had about 300 lbs of navy , kidney,red,lima and great northern seed that bugs had got into and he could not sell.Gave 'em to me. I planted beans for cover for quite a few years.