I'm not sure if WDA Products in Keswick, Ontario is even open anymore. It's been a while since we've had any information from them.
Try contacting a Kasco dealer in your area, they have props that may fit. Or maybe consider a new unit ( a 1/2 HP unit can be found for less than $550) Most people put the de-icer in before the freeze but you can cut a hole in the ice and insert the de-icer (properly mooring the device of course) and it will quickly open a huge hole in the ice. With an 8 foot depth I would use a single 1/2 HP de-icer as a best price option.
The de-icer with the thermostat control would be less than $750. You probably have a dealer in your area as the Kasco deicers are available everywhere from Ebay to Amazon.
More information on Kasco deicers and bubblers.
Regards,
The Pond Report