patrick ,
looks like a sony DX12R has a 77mm max mount -I've seen a couple on the auction site and it listed at a google search at 226.00usd
I have an old mini cam pro ring light I've used on my pentax 6x7 macro lens it was a 67 or 77 mm thread as per the brochure . I ordered the 67mm. bought it from mini cam corp of america , black diamond ,washington---long gone now.this was 20 yrs ago . current manufacture looks like the sony DX12R from what I can gather
barry