The best replacement for comfrey is arnica.

The best alternatives to comfrey are rated as following:
★★★★★  arnica
★★★★★  foxglove
★★★★  borage
★★★★  knitbone
★★★★  boneset

Your alternative for comfrey is not listed? Suggest!
Speaking about comfrey, one probably shouldn't forget about compost tea.

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



Google Trends

Scale is based on the average worldwide traffic of comfrey in all years. Click on graph for more.
comfrey
arnica
foxglove