Check out the Shopping and Fashion forum here ("Where To Find It - BC") - there are some links to shops that specifically sell fetish clothing.  Many have online stores, so if you take a peek you can see what kind of clothing is involved and maybe get a feel for what you'd like to wear.  If you're in a pinch, you can pick up some gear at either one of the two big sex shops on Davie St., "Love's Touch" and "Ultra-Love".

Dress pants, or jeans won't cut it.  A uniform is good, all-out costume is even better.  Basically, the more extreme the look, the better your chances of getting in.