You can't get the plastic minis separately from the game unless you get lucky on ebay
(people could get them during the first
KS, and some folk have broken up stuff from the game boxed too)
however if you are ok with metal and resin (and thus higher prices) you can get most of the figures from Fenris Games here (they're the company that did the sculpting work for the
KS and thus have the rights to sell these)
http://fenrisgames.com/shop#!/Cthulhu-Wars/c/6054050/offset=0&sort=normal