I’ve been looking around but haven’t found one at Thick or REI. I would need over an 8 (baseball hat size) probably closer to 8 1/4 or 8 1/2. I was going to order one online but would like to buy locally if possible plus I’m not sure which exact size it would be.
Different brands have slightly different shapes, so I would hit several local shops and try different helmets. Also the base-model for most brands is a one-size-fits-all, whereas slightly more expensive options come in sizes (which would be better for you probably).
I wear around a 7 1/2, and I’m a girl. A short one. I imagine my head looks pretty weird on my body.
(lolz at all the times that people have tried to sell me the one-size-fits-all women’s helmets — “no, it’s really adjustable, I’m sure it will fit!”)
I wear L or XL in Bern helmets, depending on the style, so those probably won’t be a good choice for you unless you can find one of the few styles that come in XXXXXXXXXXL or whatever their largest size is.
My Specialized helmet is only a Medium, though, so like Chris implied, Specialized may be a good brand for you to look at.