Where to buy Trashies / Trash Packs (Kids Toys)

We try to avoid current trendy toys and only buy them when the next fad has arrived and shops are clearing out the older ones cheap.
But… my son got given a Trash Pack toy and loves them. He's keen to build up his collection and I'd like to get some for him cheaply if possible. Ebay and gumtree - there are a few but they're not that much cheaper than retail by the time you factor in postage.
So - any ideas? Any websites that sell them cheap? Anyone seen them on sale somewhere?
Thanks for any ideas