Where can I buy perennial bean seeds (or seedlings)
If I understand you correctly, you are interested in the so-called "decorative" varieties of beans, which are grown not only for subsequent consumption, but also for the decorative appearance of the site. Varieties of perennial beans: Metcalfa, Fire red beans (Turkish beans), Red flowering, Winner, Raspberry jingle, Golden nectar, Little Red Riding Hood. The difference between the varieties in the color of the flowers and in frost resistance.
You can buy the desired variety in specialized stores selling seeds and seedlings. You can also order by mail from well-known manufacturers such as Gavrish, Aelita, Russian giant.
Before planting, in 2 weeks place the beans between wet gauze or a cloth. So more likely that it will sprout. And plant in open ground at the end of May.
If you live in the northern strip of Russia, it is better to grow seeds in small containers indoors from April to mid-May, and plant them in the ground with a lump of land in early June, when the weather is warm enough. Since beans do not tolerate temperature extremes.