Indeed dried herbs contain only a fraction of the oils, and as you said it's crucial to desiccate the plants properly to prevent bacteria/mold contamination. I think there are companies that sell plant oil extracts, usually the cheap ones are extracted using chemical solvents (thus you should not ingest these) but there are some extracted using other techniques that don't involve using nocive solvents, generally the latter are more expensive but very potent and you only need few drops to get an effect.