I do not know anywhere in Bangkok. I buy from Singapore. There are several mail order companies. I have always found this one totally reliable - Male HQ. I order Superslyde Original Silicone Lube which gets the best ratings in Australia. We like it. It has 400 ml bottles at US$54.99. Since it is over $50, the postage cost is $10 via a DHL service. But this is a DHL postal service and with covid backlogs my last order took up to about 3 weeks. The good thing is I have never had to pay any tax when it arrives in Thailand.

https://www.male-hq.com/lubes/?sort=newest&page=3