Please dont take offence, but if the car is already 20 years old fitting a new compressor is quite a big expense for a car that may not last many more years.. Even if you were able to find the part yourself at a good price it may be quite a big job to fit it and experience needed to ensure all pipe connections etc are leak free , and then getting the system regassed . Sometimes a slightly different model of compressor will fit but might need some slight modifications to the pipework, different fittings etc that an air con specialist would probably already have in stock.
If you are having the job done by a specialist they may have better and cheaper sources for obtaining the correct part ( or fast exchange if it doesnt fit ) and are more likely to guarantee their work if they supply the parts.
With a car this age it might be worth trying a DIY regassing kit that contains a leak sealant. (If they are available and permitted in Canada.) It might work, or might not but could save you 'throwing good money after bad'. Aircon professionals dont normally mention this option as its not guaranteed to work and loses them business. (Apologies if your car is immaculate and destined to become a historic museum piece
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