A strat I used was going immediately back in line to buy a small item like a deck box and hope I got a different cashier to get more packs. There's like 10 cashiers at once in the sunshine city center so you got good odds lol. Also Tokyo Station pokemon center starts selling packs at 5:00pm when everyone starts to get off work
you forgot one place. the airport. when you go through TSA and are in the airport i was able to get 5 packs of japanese 151 for 1350 yen for the bundle. only 1 bundle per person so i had my partner stand in line with me too and get a second bundle. Short story, i was in kyoto, osaka, tokyo and never got a pack. but when i was leaving the country, there was a store inside the airport selling them. Got really good pull rates too.