Paper or card stock rock walls

Try Scenic Express - they have both paper rock and paper brick walls.

Hobby stores and doll house stores

Last year, I purchased some Brick paper from a seller on Ebay.  It came from Greece of all places.  I paid $14.90 and I believe that included postage.  

Here's the words you may try putting into the search box;

11 SHEETS EMBOSSED BUMPY PAPER BRICK stone wall 21x29cm SCALE 1/43 #24D2242f

http://www.paperbrick.co.uk

Thanks for the tips.  Appreciate it.

Clever Models has some you download and print all you need.