Slag.
The moon is differentiated. Effectively, lunar regolith is ore that has been “de-ored”; all valuables have been pulled out (depleted), both by sinking to the core (siderophiles) and by degassing to space (atmophiles, some chalcophiles). Oh, and the moon is double -differentiated; Earth had already differentiated into core, crust, and mantles. Then the giant impactor struck, and a moon formed from the crust and mantle. The new body was then molten again , and differentiated AGAIN .
For bulk purposes (not part-per-million science), assume that moon rock is the crap left over from processes that are actually economic and profitable. Find yourself some industrial source that’s giving away their slag. Are you in the Great Lakes area, by any chance?
For your specific question, you would then reduce it to the relevant particle sizes. A ball mill works, but the grit would be rather rounded by comparison; actual space regoliths from airless bodies are shattered by hypervelocity impacts, and more angular. This is also the problem with volcanic ash; most ash pulled into rounder shapes while molten. I suppose some explosive volcanoes have shattered grains, but they would be mixed in with other stuff.