Sawadee nomadic ,

i think u can find @ 'Jatujak weekend market's'
u can find map @ http://www.jatujakguide.com/

they sell plant only on wed-thur

but i,m not so sure seeds are available .but they sell only plant not seeds.

plz visit mysite u may find some body who sell seed .

Here is a link that might be useful: A little Plants Collector in Thailand