Shimano derailleurs since 1997 work with 6,7, 8, 9 and 10 speed shifters and cassettes. If you aren’t intent on finding an exact replacement, you have a huge range of choices.

See the “Index Interchangeability Chart” here:
http://www.sheldonbrown.com/dura-ace.html

@jaytkay , could not get an XTR derailleur I picked up to work with the system, but it was one of those reverse-sprung models. I would like to keep the group together, but I’m more interested in fixing the shifting problems. Thanks for the tip; I should have checked Sheldon first. Hope he knows he’s still helping people where he is.