Hi Paul
I am actually looking to replace the finder on my ED80 for use with the TGAD and the ST-4 autoguider, specifically I was looking for one with a right angle erect image and Illuminator so I can place a guidestar on the rather small ST-4 chip without bending over into ridiculous angles and doing one's back in.
I found these:
http://www.stellarvue.com/f50order.html
They are available from OPT and look like they will fit the bill as far as I am concerned, they also take an 1 1/4 eyepiece, it looks like there is a specific finder bracket to fit ED80 type scopes as well.
Might be what your looking for.
Cheers
JohnG