I never buy from cons since they’re usually way overpriced and also I hate reselling doujins like that where they artists don’t see any of that money. Mostly, I buy directly from jojo events like Golden Blood but that’s pretty hard and you’d need to pay a proxy to go to the event for you and buy the books. Otherwise you can use a shopping proxy to buy from sites like Tora, the artists are the ones listing the books there.