The local Buick dealer I go to [and Kendall works for]scoured the GM warehouses around the country for rear struts for me. He entered the original number, then all the superceding ones and came up with 3 rear struts [1 in Washington and two in South Carolina] which I bought. I then found a "new" strut at a salvage yard about 80 miles from me that was in the trunk of a Reatta and never used. My brother just picked it up and yes it has never been used or installed.
I paid a premium price [full GM price] for the 3 GM struts, but only $50.00 for the "used" one so I feel a bit better.
That brings me up to the 4 I need for the Red and the 'vert [the winter Black got done about a month ago.
There are two remaining struts in a GM warehouse in South Carolina, but they are damaged but might be salvageable. You would have to go to your local dealer and see if they will get them for you. I couldn't get pictures, so have no idea what they look like.
Good luck.