What you could do – is contact the owner of that Deforest radio –
https://barrie.kijiji.ca/c-buy-and-sell- … Z186277526
It should have the same speaker – and ask them for a picture of it. From the description it sounds like its an 8 inch speaker with an extension to the frame to bring it out to either 10 or 12 inch – the field coil is 2000 ohms – the output transformer would be mounted on the speaker – and is a single ended type – you can easily obtain a universal replacement for it . The cable terminates in a 7 pin plug with 5 smaller pins and 2 fat ones – standard for pretty much all Rogers sets.
If you’re not in too much hurry for it – you could come to the next radio meet put on by the London Vintage radio club and make a connection there with someone to find a speaker – or go to the joint meet held in Guelph in the spring where you are very likely to find a scrap unit or fixer-upper.