That's odd that your bike shop doesn't carry chainring bolts. For 99.999% of the cranksets you'll encounter, all teh chainring bolts are the same size (diameter wise). The washers dont' need to be "chainring bolt specific" as long as they fit.
Finding an LBS which has both items for you saves you the hassle of looking for it yourself. But if you do need to do it, it's not rocket science.