It is difficult because it is hard to commercially grow them. You have to have more exact conditions to produce them. Terrarium types are generally from a higher altitude where the temps rarely venture far from 65-80F and humidity is ALWAYS 75% or higher. Depending on where you are located, the only place to get them are begonia meetings. go to www.begonias.org and check out the website. Greg Sytch ABS Horticultural Correspondent