Maybe nanamica? They lean more casual than dress, but I've had no problem wearing them in an office (of engineers). I've had good luck with the decent-taper-with-bigger-thighs on a few pairs. Might be worth checking out.
It fits maybe slightly smaller than a Large/Extra Large Walz cap, which, as per their website, is about 23 1/2" - 25" head size and 7 1/2 - 8 hat size. Given that, I'd say just south of 7 1/2. Stretches plenty, though, I don't think you'll have a problem.