Can you not quarantine period? Or can't have a tank set up all the time for it?
If you can do it for short periods, get 2 10g tanks at the petco $1/gal sale, an air pump, air line, airstone, and a couple ammonia alert badges. Do Tank Transfer Method (14 days)
Probably the best bet without leaving the fish in a dedicated quarantine for a long time. There are modified TTM that are supposed to protect from velvet as well.