There are comets in space, so there is water and water can be made into propellant.

Ceres also seems to have a lot of water: https://astronomy.com/news/2020/08/ceres-an-ocean-world-in-t...

Solar sails can get you to anywhere in the Solar system. Not very fast, but essentially free. So a swarm of drone ships with solar sails can transport an almost infinite amount of propellant to your refueling bases from mining sites.