I got asked a few times in the last workshop where I bought various of the materials for use in the workshop. I've linked to some of the materials via Amazon on the right hand side of the page, but I bought material from various sources - I'll link to some of the key things below:
Blank Playing cards. I've been getting these from Amazon in packs of 1,000, but smaller packs are available! These are brilliant - recommend using Sharpie "type" pens to write on the shiny surface.
Counters. Loads of different counters are available, I tend to either use these packs of transparent counters, or some slightly different opaque ones (which come in different sizes).
Blank Jigsaws. Can get these from lots of places - have bought them before from Little Crafty Bugs, who do various pack sizes of the same blank jigsaw.
Blank Game boards. I've ordered "snake style" boards from Little Crafty Bugs, but the large square boards have been from GameCrafter
Spinners, meeples / game pieces, and more... I bought lots of these from GameCrafter. This company will print your own games (I got SEEK! produced by them), but they also sell all the blanks that get printed upon. You can find a brilliant range of things on here, but be aware that the postage and packing is very expensive to the UK as they are based in the US.