This model Buick used a hydraulic lever arm type shock absorber. I did a little surfing for you to try to find rebuild kits, but didn't do any good. I did find a rebuilt unit that fits the left rear, but just the one costs $225, so if you were able to find all 4 of them, you'd have almost $1,000 invested. I know what I'd do. I'd fabricate some brackets and install conventional tube-type shock absorbers on the car.
Old Buick Parts - CARS. Inc.
Oh, and by the way, the best 50 bucks you'll ever spend on the car is to get the original factory service manual. Faxon has the 52/53 manual on CD....