I feel your pain. I was going to get a Tilley TH4, and couldn't find anything bigger than 7 5/8 in stores and so have to order it online, but haven't because I've found that while some size 7 3/4 hats will fit me others won't.

Perhaps my melon is varisized depending on how much I have on my mind at any one time... Or maybe the air pressure in my head varies with temperature... LOL

Anyway, if you're interested in something like a Tilley, which isn't exactly a booney (boonie?) then they sell size 8 and 8+ at Tilley's Endurables. They're pretty pricey though...

Oh, and they're hemp, so maybe that'll be a bonus for you. (saw your tag) LOL

I don't even want to admit that when a hat says "One Size Fits All" that I feel like a mutant when one won't fit me. LOL