Nilfisk Origin Pullman BV1100 Backpack Vacuum Cleaner Shoulder Strap Kit
Nilfisk BV1100 backpack commercial vacuum cleaner and the Nilfisk DV1100 commercial backpack vacuum cleaners shoulder strap kit of 2 shoulder pieces and plastic "I" pieces that slip through the top part of the rigid piece with the handle on it and secure with a rivet.
The complete harness is a different number and is about $140 and there are a couple of versions, depending which one you have.
These are made by Origin, and will suit many brands of backpack vacuum cleaners such as Pullman and the Nilfisk-ALTO Powervac
At the moment, standard postage is capped at a maximum of $20 within Australia, so maximise the saving on postage and buy something in the related parts below!