Dick Blick is my go-to online store for ordering supplies. They're reliable and always get the orders shipped quickly to my doorstep. Below are links to purchase materials if you need them.
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Paper & Sketchbooks
16x23 inches (tape watercolor paper to for firm backing)
Spray bottle/mister (purchase at target, Michael's)
Masking tape (Home Depot)
Large Sponge (Home Depot)