We ordered our wax for our invitations from scrapbooking-warehouse.com. I just want to say that after finishing our invitations, I am very pleased with how well the wax worked. When the wax first arrived, I was concerned that we didn't have enough because the sticks looked SO small.
We had ordered 3 packs of 6 sticks for a total of 18 sticks. We only used half of the sticks after doing 85 invitations correctly and messing up on about 5 - so 90 total. So, we actually ended up getting about 10 seals (twice as many as we had thought) from each stick. This is what our seals looked like (they were each about the size of a quarter).
To simplify things: one stick of wax from that website got us 10 quarter-sized wax seals.
We're just going to use the extra and seal our Thank You cards since we had so much fun working with the wax on the invitations!