myartandcraftsupplies.com offers a wide variety of Scrapbooking Cardstock in bulk packaging. I have not bought from them so I cannot comment on their customer service but I can tell you they have an excellent selection.
The site is a bit tricky to navigate but you’ll fins some great deals on quality cardstock names.
CORE-DINATIONS in bulk packs 20 sheets for 9.49.
Die Cuts with a View white core pack 18.99
K and Company 9.99
WorldWin – ColorMates pack of 50 20.89
WorldWin DoubleMates 36 sheets 18.99
I would be curious if anyone has bought from them- some weird things going on when I was on their site.