You have 2 mates on this forum, myself and CustomBikeMike, who have a similar problem, we don't really have much choice in helmets or the way they look, the problem is simply that almost nobody makes any that fit us at all.
We're talking XXXL.
Just FYI, while you're looking, HJC is one company that makes XXXL helmets in some styles, but not in some of the more desirable ones.
I was going to mention some styles you might try but I do notice something interesting.
They have at least one line of helmets that is available in XXXL that is DOT but they are not Snell approved.
That means they are probably made thinner.
If you are trying on a helmet in most cycle shops or anywhere that sells helmets, it's possible they don't have any helmets that are not Snell approved.
Snell standards are very extreme, much more extreme than DOT. Snell standards mandate the helmet can take a severe impact, and then take the same severe impact a second time in the same spot. Many safety engineers say the Snell standards are so unrealistic that they are causing people to suffer brain injury when there should be none.
Regardless of safety standards infighting, I'll suggest finding a cycle shop that stocks HJC, call in advance and ask if they have XXXL in models that are DOT approved only. Such as these half helmets by HJC
CL-21M
HJC-AC2M
If you can't find them anywhere else, this place is very good about returns if you do it promptly, so you could order one or more and send back the ones that don't fit.
http://leatherup.com/l/HJC-Motorcycle-Helmets/22.html