Where I can buy a same dimension of parchment paper and baking sheets? Thanks.

Last time I bought a parchment papers from Amazon and it was much large dimensions than my aluminum baking sheet. I cut some parchment paper. I thought that I can find as set of baking sheets with parchment paper without worrying to size a parchment paper.It will faster and much easier for me.

I use half sheet pans and the parchment I get is the exact size.

Agree with Dona -- the size of sheet pan you are looking for is called a "half sheet pan." That will usually fit the pre-cut sheets, which are usually for commercial use. A "cookie sheet" or "baking sheet" is not the same size. If you have a restaurant supply store in your town, you could always take one of the parchment sheets with you when you go shopping!