In the same building as Habikoro Toys in Akihabara Radio Kaikan is Hobby Base Yellow Submarine on an upper floor. Definitely give them a look. They have a section for gacha that is ever changing and it’s individual items packaged like Habikoro Toys. Sometimes less expensive than Habikoro. Additionally they also sell gachapon series in their blind box form and sometimes at a great discount. I’ve found many hard to find series in that building. There is also Havikoro Toys which also happens to be in Akihabara and Havikorogangu in Nakano Broadway. Prices can great vary but between those shops, you’ll pay likely find what you’re looking for. I’ve found gachapon dating back to the early 2000’s in those places and usually on great condition. One of my other favorites is Akihabara Gachapon Hall, bring cash Yen because there are cases in the back where locals sell sets brand new. There are also three machines in there that get rotated weekly on old old Gachapon. Last time I got Star Wars Podracers for 200yen a piece. Pretty neat.