I know you asked for SU, but if you are willing to go afield and just google dandelion rubber stamp a ton will come up...in fact I just put two into my wishlist from England in case I find them here plus one from Beeswax that is bontanically oriented.
at SSS
dandelion stamp at Simon Says STAMP!
at Etsy -I am going to surf this myself bc I already saw an extra large seed stamp
Dandelion rubber stamp | Etsy
they have always been around but seem to me got popular in the past year.