Ski Chalet is in Gaithersburg - off 270 on the way up to the PA resorts. They have good rentals/demos.

BTW: if you're going to try skiboarding , you might want to think about a helmet, too Have fun!

Looking for a decent (yet reasonable) ski/board shop in the Silver Spring/Bethesda/Rockville area to rent skis (possible ski blades too)and purchase ski pants. Thanks.

Ski Center in northwest DC is an excellent shop for many reasons - but may not fit your definition of "reasonable."

www.skicenter.com

To just get clothing and not rent equipment:

Sports Authority on Rockville Pike usually carries Columbia clothing and is probably your best bet for saving money on clothing.
In my experience, Ski Chalet and Ski Center generally carry higher end clothing.

Never been there, but you might also try Galyan's off of 270 near the now defunct Sportland.

Good Luck

You may also want to think about getting wrist guards. Number one injury among snowboarders occurs in the wrists (sprains/fractures) - due to falling with your hands forward (instinctive reaction).