It's great to hear you getting into mason bees.
Mud can be provided if none is found naturally. You can get mud and make a make-shift container out of a trash can lid, dinner plate, etc. If you sink the plate into the soil, then let the water fill the plate and run off, this has worked for me in the past. A dripping hose, or better yet, one that seeps water into the mud will work fine. A dripping faucet can also provide a place for butterflies and other insects to drink.
Masons will only travel in about a 200-300 yard range from their home. If you have a stream or pond, nothing else is needed, as they will find mud. But if not, you must provide it for them. Masons need three things to thrive. Adequate housing, a chemical free source of early flowing trees (fruit.... but not required), and mud. If they do not have these three requirements, the mason bees will move on to better pasture.