You can substitute pumice for perlite.

I've substituted diatomaceous earth (some kind of Napa Floor Dry, I think) for perlite. I've seen concerns that that product might not hold up, but mine held its shape in containers for a few years. At the end of its life I could squish pieces of it between my fingers if I tried, but the soil was more impacted from decomposed bark than the DE. Results might be different in freezing temps.

I like perlite more than I used to. I still don't like how it floats to the surface, but I like how light it is, and I think some roots do, too. Can't speak to Japanese maples though. Good luck. :)

Thanks both of you for the input..

Fievel - what's most appropriate will depend on what other ingredients make up the soil, their size (primarily bark size), and at what ratio they're mixed. There is nothing to stop you from using plenty of grit or perlite mixed into the bottom several inches of soil and Turface or an equal in the upper part of the soil. This would reduce the volume of water in the PWT and increase water retention (at no expense to aeration or drainage) in the upper reaches of soil - above the PWT line.

Al