I have a massive dome as well, and ordering caps online has been a bitch for me. For reference, 7 3/4 New Era's fit quite tight for me and would leave a massive mark on my forehead. I always got those because stores around here didn't carry the bigger sizes (and they looked quite ridiculous on my already comically large head)
Strapback Theories hats fit me well pretty much all the time. Their snapbacks, not so much. I recently bought a Baker strapback, the green one with the "B" rivet on it. It fits perfectly and has a lot of extra room.
Most Polar strapbacks fit great for me, even their snapbacks fit.
I've had some Magenta strap backs fit, some were too small. Their snapbacks are def. too small for me. Their five panels fit me, which is odd because most 5 panels don't fit me.
I have a 917 strapback that fits (the blue one Roger wears from time to time), but the strap is at its max, I can only really wear it with a shaved head/short hair, or else it gets too tight.
No Huf hats have ever fit me. The new Alien Workshop hats don't fit my massive dome at all either.
i want to try the Hopps lion strapback, but with the price conversion + customs, I don't want to end up with a hat that's too small, it's always a bitch to return.
Hope this helps, as a hat guy with a big-ass head, I feel your pain.