Thanks Biff- Here it is without the plastic face plate- It's a Paradigm part B3TWHF-TIM-090. I found one palce that said they could get it for about $100 which seems steep so I'd like to try an aftermarket that might even be better.
All Paradigm parts are made in Canada- great stuff and one of the last (and best) remaining legacies of the great drive in Canadian acoustic research of the 60's and 70's. they are great value and I get that warm fuzzy feeling of buying Canadian made home electronics that don't cost a small fortune- it's like finding a Dodo bird if dodo birds were cheap and sounded good.
Oh yeah- the dome is 26mm and the magnet is 68mm