Perhaps we could be of more assistance, if we knew what models you are looking for. Having looked at the Cult list in the Army Compendium, I guess you are looking for proxies for the standard Guard vehicles. My best advice would be to look at the function of the unit, and start searching for suitable proxies. There are plenty of good 6mm manufaturers nowadays, so there are plenty of fun models. Since it is a cult uprising, non-standard vehicles might suit you better anyway. I know that is the way I am heading with my Chaos Cultists.
For instance:
Leeman Russ - main battle tank
Chimera - APC
Basilisk: self-propelled artillery
Hydra - self-propelled anti-air
Sentinels - scout vehicle (walkers are in short supply)
Civilian vehicles - these are the hardest. I find most 6mm trucks are a bit on the small side. I loved uvenlords(?) mixing of old-school battlewagonz with truck bits. Onslaught Miniatures has something down the pipeline, but I do not know what, yet.
So, in Exodus Wars:
Battle Tank: Achilles
http://www.steelcrowngames.com/products ... t-squadronChimera: Phalanx APC
http://www.steelcrowngames.com/products ... c-squadronBasilisk: Apollo
http://www.steelcrowngames.com/products ... pa-batteryHydra: Icharus
http://www.steelcrowngames.com/products ... ag-batteryScout vehicles: Agamemnon
http://www.steelcrowngames.com/products ... detachmentOther good companies for your needs are:
Dark Realm
Microworld Games
Brigade
Troublemaker Games (the upcoming plastic/metals should cover Chimeras/Basilisks/Hydras)