Assuming you had your brew in a decently "safe" place like a closet you should probably be alright. Next time this happens I would sanitize a piece of aluminum foil and stick it over the hole where your airlock would go. If its only going to be a few hours before you can get an airlock, go ahead and pitch the yeast, as the sooner you start fermenting, the better your chances of avoiding infection.
Funny you start this thread. SWMBO is rushing to the LHBS for me tomorrow (while I brew) to get me a new 3 piece airlock. I threw the old one away when I got a new plastic 7.9 gallon fermentor to replace my old 6.5 gallon that I used for almost 3 years. I plan on doing the whole "aluminum foil" deal myself should she not arrive in time.