Looking for Nettles can they be started from seed?
Hehe.........I can show you many, many patches of nettles! You would then be free to wade in and gather all the seed you want!
Seriously though, I am sure the varioous nettles will come from seed. They readily colonize new ground in nature.
Which species are you interested in? Here we've got tall nettle, woodland nettle, and at least a couple others. I don't hate these plants. Some don't believe it but not only are the nettles native plants, but some lepidopterous insect species (Butterflys) absolutely require nettle plants in order to complete their lifecycles. Perhaps that is your interest.
I was able to get seeds from stinging nettles from another generous member on the butterfly forum. I've wintersown one container of them, but I still have lots of seeds.