You can buy mice for 3 months before going home, pack them in a styrofoam box with ice or a portable fridge (like the ones to go to beach or camp) and take them with you, then put them in the normal freezer.
I'm in a similar situation, though. I live 1h away from the capital, which is the only place for me to get the correct sized mice. I buy like 10 live ones online, sometimes personally go buy there, and then I euthanase them at home and freeze them. I know euthanasing animals is not what you want to do, no one does, but it's an option to consider. Plus you can feed freshly prekilled if the shop is near enough to go every week.