From holland !!!
They are first year tubers...
They get them small and cheap.
Try antonelli's begonias. They have a store on ebay, too

Seems to me back in the dark ages when I was young and lived in a climate where I could grow tuberous begonias that some people preferred the small tubers, or even to start them from seed themselves each year, because they claimed the small tubers gave bigger flowers than the larger older tubers. I'm sure the plants would be smaller so there would be less blooms though. Don't recall doing any testing myself to see if that was true.

Thankyou both for replying , it's hard to imagine that anything so small and light will produce what I want, but after all...how big is a seed !

Begonia seeds are in the 'dust-like' category. I've grown a lot of things from seed, but I must admit begonia seed (and gesneriads, another addiction of mine) are kind of scary to me. Gonna have to try some, maybe this year!