Thank you all for the links and advices.
For now, I think rebelminis 's got the best range to adapt. Probably some re-sculpting there and there, but...
edit : I just made some further researchs, helped with other guys on 2HW yahoo group, and found a lot of interesting references in GZG miniatures range ! Colonists, techs, etc... will make really cool Bad guy minions. Some civilians will do cool sidekicks too.