Hi there. I did a bit of searching and came across the standard
assortment of stock photography sites, all of which charge upwards of
$50 for high-res images of the size you need.
I did, however, find the following site:
They provide a myriad of textures, each available in two sizes (low
and high resolutions). I ran a search on their site for "leather" and
the engine showed me a number of textures, six or seven of which
should be useful for you. Strangely, there is no standard size for
their textures, and so some of them don't quite reach 8.5x11 @ 300
DPI. However, there are several that meet that requirement,
Black Leather (3500x2993 = roughly 10"x11.5")
Green Leather (2946x3500 = roughly 11.5"x10")
Darkbrown Tileable Leather (1364x1364, but repeatable to get your size)
Perforated Leather 2 (3500x3423 = roughly 11.5"x11.5")
Each of these costs 7 EUR (so, about $8.50 apiece).
Please let me know if I can be of more assistance.
'leather textures resolution'