G'day Ben,
I was put onto a cheapish brand of gloves by Stephen Polzin (member of this site), called "Medalist". They are available through BCF, well that's where I got mine, and while my mits are probably not quite as large as yours, these gloves fit me easily with room to spare, and provide good protection for all types of heavy popper casting, fish handling etc.
They are also pretty ugly (bright orange), but if functionality is your only concern, then they might be worth a look.
Pic attached below...
Cheers
Angus