The best replacement for pumice is perlite.

The best alternatives to pumice are rated as following:
★★★★★  perlite
★★★  obsidian
★★★  vermiculite
★★  scoria
★  lava rock
★  tuff
★  turface
  basalt

Your alternative for pumice is not listed? Suggest!
Speaking about pumice, one probably shouldn't forget about nail brush.

Other search terms related to pumice and their ratings are:
★★★★★ nail brush
You have in mind a companion for pumice and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of pumice in all years. Click on graph for more.
pumice
perlite
obsidian