Quick post to share how I've searched in the past for temperate climate seeds of the unusual perennial vegetables & food forest plants. I haven't done much with these for more than a year, but in the past I mainly used two plant search engines:
Dave's Garden Plant Scout (returns more live plant sources)
Plant Information Online from the University of Minnesota (returns more seed sources)
A few years ago when I was most actively seeking seeds, I made a list of everything I wanted, and wrote some scripts to automatically search for each plant at the Dave's Garden Plant Scout site, then parse the results and put them into a spreadsheet for me. Then I went through the spreadsheet manually to order most of my desired seeds from about a dozen companies. You can download the resulting spreadsheet to see what seed companies were useful to me in the past.