dreads compete w/helmets...
I have dreads and when I started riding, I had the same problem and I found this forum doing a search for a solution to this problem seeing as though i'm now in need of a new helmet. I went with an HJC because it fit the best, but the selection was limited to only a couple options anyway. The salesman in the store also suggested the option of cutting off my dreads, or cutting them on just the sides, both are things that I still can't bring myself to do but he made a very good point:
The purpose of the helmet fitting properly is so that it doesn't slip around on your head in the case that you go down. But if you do wreck, the dreadlocks that are requiring you to wear a helmet 1 or 2 sizes too large will likely shift, tear, smash, whatever, and the helmet will act accordingly, possibly foregoing the protection that it was originally intended to provide. The other thing that I noticed with dreads is that they tended to push the front of the of the helmet towards my chin which wouldn't be good in a crash either.
Anyway, the last time I picked one out I tried a few xxl/xxxl helmets on in the store to accommodate for my big a** head+dreadlocks. I bought the HJC one and lived with it but since 3 years have gone by, including one wreck where the helmet did make contact with the ground (minor scratches, but still), I'm looking for a new helmet and am back in the same boat.