Try looking here for scanned samples of fabric:

http://www.tartanweb.org/ancient/gow.html

http://www.tartanweb.org/modern/gow.html

http://www.tartanweb.org/weathered/gow.html

http://www.tartanweb.org/ancient/smith.html

http://www.tartanweb.org/modern/smith.html

http://www.tartanweb.org/muted/smith.html

http://www.tartanweb.org/weathered/smith.html