best suggestion I have is using Cadians with some Pig Iron heads:
http://www.thecombatcompany.com.au//shopexd.asp?id=4156
http://www.thecombatcompany.com.au//shopexd.asp?id=4159
Just a few examples of heads you could use.
and a simple weapon swap/conversion to replace the lasguns with shotguns.
Even by shortening/removing the barrel on the lasgun it makes for a pretty decent looking
shotgun.
If you want them to have riot shields and power maul you could use:
http://www.maxmini.eu/store/index.php?main_page=product_info&cPath=12&products_id=47
Dunno how you could make power mauls, maybe just a simple stick of plastic with some greenstuff additions.
............. and thats my two cents! good luck :-)
edit - I just realised - this will probably set you back about $60-80 anyway :-P If you are only after one arbites looking model,
eBay will be your friend ;-) Usually you can get a single arbites model for around $15-20 delivered.