Your local parts store like NAPA or similar should be able to help.
You do know to ask for 61 Chevrolet, not Pontiac? Some books will not list Canadian Pontiac and if they give you US Pontiac ball joints you will be returning them!
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1966 Strato Chief 2 door, 427 4 speed, 45,000 original miles
1966 Grande Parisienne, 396 1 of 23 factory air cars (now converted to a "factory" 4 speed)
I always use AC Delco stuff on my vehicles (because I've made my living selling it for the past 37 years!) and have been very happy with it. Maybe you have a local parts store that sells AC stuff.
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1966 Strato Chief 2 door, 427 4 speed, 45,000 original miles
1966 Grande Parisienne, 396 1 of 23 factory air cars (now converted to a "factory" 4 speed)
They are on rockauto.com for $37.81 cdn for the lowers and $59.58 for the uppers. Plus shipping, of course. They aren't listed under the Pontiacs but rather 61 Biscayne. They have a different AC number but cross reference to the numbers Carl gave you.