I need advice on what kind of soil I can get for my seedlings. Miracle Gro is crap. It does not dry out for a very long time, and it came with fungus gnats.

Is there a good potting soil for tree seedlings, or should I make my own?

I use hasselfors garden seed sowing and cactus mix. Very happy with that product.

Leaf mold has been working pretty well for a couple of million years. 

That's a good idea. It's a very easy version of compost. Thank you!

My preferred soil for my trees is either Akadama and pumice 50/50 or just Akadama. For growing on any multipurpose product will do.