How about an old agricultural grain drying/blowing fan?

Megacycles,

Can you describe the modification so we dont have to re-invent the wheel (blower).

The leaf blower I used could suck and blow so the first thing I did was araldite the flap which allows the changeover so the machine can only suck. This stops any small airflow that could leak into the blow tube (its very rudimentary inside) which would blow dust everywhere.

Then a rummage through the local vacuum cleaner repair shop yielded the perfect fitting to screw and seal over the blower outlet where the collection bag normally attaches. Its easy then to connect up standard vacuum cleaner hoses.

All very agricultural but I managed to get around 240kg into the walls but the motor needed running repairs toward the end to make it as the dust gets everywhere, so its only suitable for smaller jobs. I found the fan really chopped the warmcel up but it needs a pre-breakup first.

Initially I calculated the volume of the voids and measured what weight of warmcel that went in to fill it. It was usually around the recommended 35kg/m3 so I'm confident it worked ok, just a bit slow

The only blowers that I could find in UK I think are imported by Excel so its unlikely they will be available for hire. I checked all the local hire shops but got nowhere. So fostertom is right, theres no competition and prices are very expensive.