Check out any online biking stores (jenson usa, chain reaction cycles, wheelworld, huck n' roll, etc) & look for "mountain biking shorts" (will probably be under apparel>short>mountain, or something to that nature). Make sure whatever you decide on has what is called a 'chamois', as this is the liner than has the padding to keep your butt from hurting so much after long rides. The chamois liner will be skin-tight...that's just a part of biking shorts...but the exterior will look just like a regular pair of shorts.