Specifically, season 11 filmed in Concord, Ma starting in October 1989
episodes 901-920. The segments were of a timber frame barn that Tedd
Benson decided needed a total rebuilding. It is commonly called the
"Concord Barn" or "Concord Project". "This Old House" is a production
of WGBH, a PBS station. Officially these shows are not for sale. Where
do they exist? In this day of instant access, I am frustrated that I
can not find any copies, even more so because in 1989 they were
available for sale. This is one of their most popular seasons.

I have exhausted my resources and can not locate a copy for viewing or
buying. I have heard they recently reaired the show and revisited the
site this summer sometime but I'm not sure of this information. The
Library of Congress does not seem to own a copy. Where can I locate a
copy for viewing or sale? Thanks so much.

Here is the official site describing the project:

http://www.thisoldhouse.com/toh/tvprograms/houseproject/overview/0,16542,197946,00.html

other than moving pics it seems to have everything you would ever want to know.