I reuse brake crush washers all the time. In fact, it's a pain to find any place that actually sells the stupid things. I happened to buy something else at Z1 Enterprises awhile back and saw that they had 10 packs of them so I ordered a set since the extra shipping costs would be zip. I've asked before at dealers or at places like Cycle Gear and they all look at me funny. "Crush washers"? What are crush washers? Nope. We don't have any of those...
So when I part out old bike I keep the banjo junction boxes from the front brake lines. Great source of extra crush washers and banjo bolts.
TR