Check out www.paintscratch.com - they have the colors listed. Perhaps the color you want is Crystal Blue Poly? There is also Cascade Blue Poly and Stratomist Blue Poly.
http://www.tcpglobal.com/autocolorlibrary/aclchip.aspx?image=1972-buick-pg01.jpg I would say Chrystal blue Poly as well
check the data plate on the cowl. 21=Crystal 24=Cascade 26=Stratomist my Suncoupe in my avatar is Cascade.
That sure looks like Stratomist Blue from the pics, especially comparing it to the light blue door jamb sticker.