I am having trouble finding a nice white cotton paper texture. It is very common in printwork. This will be for commercial work. Also, how would I go about creating the texture myself? i.e, buy cotton paper and just take a photo?
A good quality scan is the usual approach. The problem tends to be that because the lighting is flat and the contrast (especially with bright white paper) is low, the texture may not "read" well. It's the simplest approach, though, and if it works out, you're done.
Many print shops and all paper manufacturers will be only too happy to send you sample sheets, so you probably won't have to buy a box just to do one scan or photograph.
Oblique lighting is how you bring out texture photographically. That creates its own problem of light fall-off from one side to the other on a very flat, even surface, which will be exaggerated in the photograph. You'll want to move the light source far enough away from the paper to get within about 1/4 stop difference between the edges.
It takes a bit of experimenting with the light (a large, diffuse light shows less texture, but less fall-off than a smaller one), the angle (a sharper angle shows more texture but increases the amount of fall-off) and the lens (any vignetting will be more obvious on an even white field). A good, solid tripod, pin-sharp focus and a cable release or delay timer are essential, and you will find that a polarizing filter helps a lot.
Digital capture of high-frequency information like this requires plenty of megapixels, a large sensor and the best lens you can get your hands on. The idea is to get as good a capture as possible so you have minimal correction to do in Photoshop. Get a raw capture, not a jpeg, and do your post in Adobe Camera Raw or Capture One for the best result with the least pain.
A bit of attention to what is behind your paper sample is worthwhile. A mid-to-dark (neutral!) backing can let the translucency of some papers, especially "linen" and some cotton rag papers, work in your favor to bring out texture. This applies to a scan or a photograph.