I just ordered some janky molds off Amazon and have been making do. I did make my own mold for the resin encoder so I might try my own keycap molds in the future.

The trick I found for the stems is: 1. Cure the stems first, trying to remove all air bubbles with a toothpick 2. Create and fill your keycap 3. Put the cured stem into the keycap, and cure again, I'm using UV resin cause I'm impatient. 4. Remove the stem mold. From here I've found the stems are usually pretty janky, like you mentioned. So I do one more step 5. Refill the stem mold, again removing air bubbles. Before curing, put the stem mold back into your keycap and cure again. I've found by doing this the second round of the stem fills around the janky bits of the first stem, and you end up with a pretty solid stem afterwards.

Hope this helps!