My friend in high school had a dark green & tan 68 ragtop - what a car ! I never got a ride in it though - we parted as friends during Sr year.
You've seemed to have covered all the bases so far in your search. These cars were low production cars when new making it more difficult to find parts almost 40 years later.
On several trips this summer I did notice lot of old 50's - 70s auto's sitting on peoples property with 4 foot high weeds grown up around them. I can't understand the logic of letting all those cars just sit there. When you could sell them whole or for parts.
In Chicago you got to have a current licesne plate registration & city sticker for non - running cars sitting on your property. If not you don't want to comply you will have to get rid of it.
In Minnesota last week I saw a lite green 68 Caprice Estate Wagon ( woodie ) that looked absolutely amazing & all body trim intact, it surrounded on two sides by high weeds parked next to the garage.
Good Luck
Harryface
05 Park Avenue, 26,122
91 Bonneville LE 303,568