I assume that you're using a backing sheet, or two?

​The first step would be to use a liberal amount of rubber rejuvenator on the platen, which can soften the rubber a little - sometimes enough to make a difference if your platen isn't extremely hard.

No. I spray the rejuvenator onto a piece of paper towel that has been folded many time to form a thick pad and then wipe it back and forth on the platen as I turn it. I don't recommend spraying directly on the platen as any overspray - and it will happen - can damage paint. You may need to repeat this process up to a dozen times before you'll begin to soften things enough to make a difference. I can speak from experience that it will work with platens that are in the 93A to 97A range; even though there isn't much hope for platens harder than 97A (they shouldn't be used), I always try the rejuvenator anyway.

I get mine from justonecable.ca and typically order several cans at a time for pick it up from their warehouse (DVP and Lawrence area). It is (was) around $6 + taxes per can. I have an extra can on the shelf if ordering through them is too much of a hassle for you. 

I'd suggest giving them a call; if its out of stock they'll notify you when it's available again.

I have ordered two cans of Blow Off from Upper Canada; don't know when they will reach me by the postal service.

Does the lack of suggestions mean there are NO tradesmen who will recover a platen in Canada?