I'd go to any art supplies store and look in the stationery section, you'll find lots of options in there. Lately I bought some Pantone notepads, they come in

I'd go to any art supplies store and look in the stationery section, you'll find lots of options in there. Lately I bought some Pantone notepads, they come in several sizes, sturdy and have dotted guides. But 99% of the time I just use cheap 99¢ notebooks.