First you should tell us which period of the cold war are you modeling...
also there is no thing as 'woodland' in US vehicles. You have the MRDC scheme in two variants used in Europe, then the CARC green (usually on M1 and M2/3 basically new vehicles waiting for the NATO 3 color scheme officialization) and the Nato three color scheme coming into service from 1984-85 onward.
The soviet tend to be in green, but there are some variations according to Group of Forces (Germany or Central). WP members had national approach to camo.
I know nothing about 'free' sources (except researching vehicle image on the net) but I know several good ones.
A good source for US Army vehicles are the various Tankograd books, especially the one on Reforger exercises. The Osprey New Vanguard on T-62, T-72, T-64 and T-80 have also good profile and pictures, as the new books on the T-54, T-55 and T-62 by Sewell (they a re a bit pricey just for a color scheme too... but they are very good).