No problem, it was just a simple phone call to get the confirmation of opening days/times. Chatuchak plant/flower market is predominately a plant market, but I'm sure that I've seen a few stalls selling seeds.

If you PM me with what seeds your after I'll pop to our local market (Sanam Luang 2 which is open every day and has a far larger selection of plants than Chatuchak) and have a look at what they have. No doubt if the seeds you want are available at Sanam Luang 2 they may well be available at Chatuchak.