Pixels aren't sold in Thailand, at least not officially in shops. I bought my Pixel 6 & 7 here through Lazada and the new Pixel 9 on Shopee. It's always a bit of a gamble buying that way. Also, they come with the regular android OS loaded, so you still need to either install GOS yourself or get a phone repair shop to help. Also, new pixels are expensive, so unless you really need one of the latest models, it might be better to go for model 6 or 7, rather than the newer ones. If you search the internet, you can get pixels with GOS pre-installed but you might have to order from Singapore or the USA. I haven't looked but I imagine you might be able to buy a Pixel older model 'reconditioned' and for sale with GOS preinstalled. You just might have to pay the duty on it when it arrives. There are several sellers around the world who ship phones with similar but not identical privacy/security type Operating Systems. Some sell other brand-name phones, but a lot stick with the Pixel models, because it has the most secure hardware and it is still designed so another OS (ROM) can be easily installed. I had a phone with CalyxOS on it and I was very happy with it. Best to do a web search for what's available if you're open to an alternative to Graphene/Pixel.
Sorry, I'm not being much help, but I just haven't found anything here in CM or within Thailand, but then I've been fairly comfortable ordering online & installing GOS myself after delivery.