Any ideas where to buy? im located in Phuket, not that the location should matter 

Search the Farming in Thailand forum and especially the Organic subforum, where there have been several discussions over the years on this subject. I don't have personal experience buying heirloom tomato seeds, but I know that there are some experienced growers who may be able to give you some recommendations. Good luck.

 

Here's one suggestion from a discussion last year:

I've ordered from plant-world-seeds.com a few times and haven't had a single problem with them, the seeds or deliveries. 

Thanks for the link, I have ordered and made payment so just wait and see for the delivery.

They have a great selection so hopefully all goes well.

thanks