I used to use 9.5 x 12.5 paper, Wausau Exact Index, 110 lb in white. If you can find something similar in an ivory, that would be a little easier on the eyes. But white is much easier to find.

I just called a couple local printers and told them what I needed. One printer offered to get it for me, but he tacked on a large fee for himself. Another printer gave me the name and number of his supplier. I contacted them directly, they did a custom cut for my size. The only downside is it's better to make a large order, keeps the cost per page down. I would order once a year anywhere between 2,000 - 5,000 sheets at a time. It just depended how busy I was. Also, buy locally I didn't have any shipping costs.

I'm sure there are other brands and weights of paper that will work for you also, but I hope this helps you as a starting point/

9x12 is one half of 12 x 18 aka "Super Tabloid", a standard size that is readily available. 13 x 19 is also known as "Super Tabloid" which gets a little confusing.

Any real print shop can get it for you by doing a custom cut — it's a standard service though prices will vary widely. Don't confuse the local copy place with a real print shop.

If your needs aren't that large, buy 12 x 18 and a good office paper cutter. Make your own.