there are some organic pest sprays that you can use up til the day of harvest, like the brand Safers. (you would probably want to spray your plants down with water the day after tho, to wash it off)

other options: put plants outside for about 20mins to freeze the buggers off; or try misting plants with water...i hear spider mites don't like humidity. just be careful your plants are able to dry off well afterwards, you don't want bud mold.