They
are refillable. Just bring 'em to the park. I bring mine several times a week. Trust me. That poor cup has been left on the MIB ride so many times that I can't count but I have my name written on it so the ride operators just save it for me. One time Slacking even found it on a MIB car and recognized it as mine!
I had one MIB cup for a year and finally lost it for good. I bought another one just like it and have had it nearly a year now and use it several times a week at the parks. It is old and has been through the dishwasher so many times that the MIB symbols are peeling off and like I mentioned before I have my last name written in big letters with permanent marker.
No problem at all getting it refilled.