Yeah, it's plate mounted, you can get brown switches from some Cherry G80-8xxx series boards, rawko may still have some on ebay. You'll have to desolder the switches from the BW, pop the top part of the switch off, pop the switches from the Cherry board (no desoldering on that one) replace stems, resolder switches on the blackwidow.
That's the cheapest way to do it, as buying browns would cost about a dollar a switch, and the BW has 109 switches, if I remember correctly.