Ah. Not the easiest thing to do for me. There should be a mod that makes building a particle on the ground accelerator possible and produce antimatter without going into space. There could be large rovers ferrying antimatter containers to another structure which can be upgraded by adding more antimatter containers to it. Since, in 0.23, the player has the ability to modify the amount of fuel a craft launches with they can add some antimatter to the antimatter tanks on their crafts. There can be a display inside the construction buildings which shows the amount of antimatter left in the collection building. A way to balance this could be the necessity to add generators to the building as the antimatter capacity increases.
