I dont know anymore the answer to your question or if they are even still available but I can tell you that if your looking to buy a juice bucket and boost the quality with it that after shipping and the skins themselve youd be better off just buying a high end kit to begin with and 99% of the time youll get a much better wine anyway. If your looking for a cheaper wine kit with skins look at Cellar Craft and RJ Spagnols as they both make 2 or more levels of quality with skin kits.
There are grape skin packs available from Paklab on EBay. Others have discussed buying a lug or two of fresh grapes in season and crushing by hand and freezing.
G-funk, search "Fior D'uva" on eBay. They sell four packs for about $80 and eight packs for about $155 with shipping included. They have three varieties, Cabernet Sauvignon, Merlot and Shiraz and the packs are 2.2 Kg.