I had known about Etsy for a few years now but I never thought of buying supplies there. I wish I had known much sooner! Paper packs seem to be more popular that whole sheets. There are handmade embellishments, buttons, brads, tins, ribbon, and sooooo much more!
In the search bar, you have to drop down to supplies to search supplies. It's not the best system, but it doesn't clog the handmade with supplies so they should be easier to find.
I sell paper packs, die cuts, silk flowers, and sometimes some extra eyelets and brads. I love to destash on Etsy. I love to buy as well since the costs seem to be lower than ebay and the shipping prices seem to be a lot more reasonable.