I've got a really cheap Robinsons one in XF but it is HUGE - dwarfs the head of my 17hh! I also have a Cottage Craft one, padded with fluffy stuff, which is quite a nice fit.
My friends ID has got a large head and he wears a XF in bridle but he does fit into a full head collar that the local tack shop sells, but to be honest they are massive
The best quality v large headcollar I have found is made by John Whitaker. It also has a very very good quality leadrope (long). Mind you, mine is getting on a bit, it has lasted 5 years already! It fits my 17hh Irish Draught donkey (supposed to be x TB but his head didnt get much of a sniff of the TB bottle I dont think!)