Sure, hundreds! Use anything you like! Their actual efficacy is another matter however. There are all kinds of stories out there about momily magic bullets, several that seem plausible but are unproven, but really the current fight against varroa is pretty well studied. And I'm afraid onions haven't yet made the cut (har har).
Now if you're looking for "soft" treatments, we all need to reconsider the word "chemical". It doesn't really have an objective definition in this sense, but if often used pejoratively by people looking to avoid synthetic miticides. Thymol for example (several commercial anti-varroa products) is just essential oil of thyme. Chemical? Technically, but so is water . Organic? Yep, and effective too.
Consider learning about Integrated Pest Management; it's what sustainable beekeeping (and indeed sustaiable agriculture) is all about. You'll be able to try what methods seem doable to you, and evaluate for yourself their effectiveness. But use things that either have been tried and prove, might plausibly have a mechanism for working, or just seem interesting (but be prepared to lose a lot of bees). There are lots of mechanical, cultural, genetic, soft-treatment and other methods to try before giving up eggplant because your bees need it .
Bees, brews and fun
in Lyons, CO