I well remember getting those big Polish cats, dogs, dinosaurs, stamps on mail from Polish relatives in the mid 60's. As a schoolboy they were wonderful. Yes, they were aimed at the philatelic market, but they were also massively used.
The communist countries from the 60's onwards is what you want for large colourful stamps. The market for this sort of material is virtually non-existant now, there's a mass of this era on
ebay & Delcampe & I would recommend buying collections as the most economical way of acquiring these. Make sure to have a look at Czechoslovakia from this period - wonderfully engraved.
Here's a link to Ben's Poland site to see what's out there. The large stamps start about 1960
http://www.stampspoland.nl/