Do they sell mangosteen (山竹)(มังคุด)? I didn't see any last time I was there. If so, what time of year is best and where can I find them in the store?

The summer months are the season for mangosteen there ready between April and July, I personally haven't seen them for sale in china town for quite some time but when I did see them last it was sold from street vendors. I was in Thailand last summer and ate a ton of them there very delicious. I do hope that you find them.

By grand street and Bowery u can find it