There was a thread on here somewhere about wads.

Try fibre board from the builders merchants. It is used for expansion joints in concrete. It comes in 3/8" & 1/2" thickness and the sheets are, I think 8'x4', but if you can get broken ones they will be a lot cheaper.
I noticed that it looked very similar to eley fibre wads so I did some experimenting and it convinced me that it was the same stuff.
I stamped some out with a wad punch and then lightly greased the wads with beeswax and tallow and they worked ok in 12 bore shotgun cartridges.

Good luck.