Any recommendation for somewhere that sells bamboo seeds?

looking specifically for Gigantochloa andamanesis

Do you really want to grow from seeds? I've never tried bamboo, but internet wisdom (yeah, I know) has bamboo as less than easy to get started.

 

Small plants from the plant-man or cuttings from an established plant are the easy option ?

 

When the bamboo Fargesia nitida started blooming about 40 years ago, it was the first time for 120 years, over a period of about 30 years they ALL bloomed, all over the world, and ALL died. (I had sold about one thousand a year or so before this started!). The seeds I took all germinated and all eventually died, although some people did manage to cultivate and produce new cultivars.

Dunno about your particular bamboo but unless it has bloomed recently you won't find many seeds.

I have never a seen bamboo blooming here in Thailand, it is an infrequent occurrence and was deemed to be unlucky, as the rats, having eaten the seeds, then descended on the rice fields.

Anyway, the tropical bamboos are generally easy to start from "cuttings" (one metre long pieces 8 - 12 cm thick, rammed into the ground). Done that.