If it has a flat base, as opposed to feet, do it yourself. You can buy castors on small metal plates and you just screw them to the base. With small, sharp screws you don't even have to pre-drill - as long as you have an electric or battery powered screw driver.
Even easier if you have wooden or tiled floors is to attach to the base some of those self adhesive round felt pads you can buy in small sheets in IKEA. I've done this to sets of drawers in our bedrooms and they slide about very easily.