There was a good thread on zeolite a few years ago that is maybe worth revisiting.
IIRC Zeolites aren’t readily available in the US but maybe there are some sources out there.
Before getting into bonsai, I got some of this zeolite mix for houseplants. It was pretty good, but maybe a bit pricy (especially compared to garden center soil) so I stopped buying it but worked well. Every so often I think about buying another bag just to see how it would stand up with bonsai.
https://www.lechuza.us/accessories-lechuza-pon/lechuza-pon-1.4-us.dry.gal/19561.html
From the website the mix is:
- Zeolite
- German washed pumice
- German, light Lava (permanently supplies your plant with iron)
- Fully-coated, premium-quality fertilizer.
- The coating is purely organize and breaks down without leaving any residue.
- The fertilizer supplies your plant with nutrients for up to 6 months.
- Fit for all plants, including foliage, flowering plants like orchids, citrus plants, herbs, tomatoes, fruit trees, cacti, and more.