Norman
Congradulations for growing that monster onion. You sure do things big in BC.
The answer to your quest was at your finger tips SEARCH
Here is a repeat of the brief description of that wonderful tool for the avid gardener or Tim the Toolman type that you asked about ......an ELECTRIC VIBRATING SIEVE.
It is a homemade contraption that you can easily assemble in an hour or so with material from home or your local building supplier. Dimensions could be reduced according to your needs and ability to store. I make about two cubic yards of the most beautiful compost with it every year and it is a good size for my needs. Briefly: Nail together a rectangular box ~two feet by five feet. With roofing nails,secure a piece of galvanized diamond mesh to this box. Nail two struts with a plywood cross brace Bolt on an old electric motor(eg from furnace blower) to the top of the box. Drill a hole in the pulley and tightly fasten a large bolt. This off-balance pulley causes the box to vibrate when the motor is plugged in. Again.. ensure that bolt is tight. You don't want NASA wondering where that new satellite came from.
Compost can be sieved directly into a wheelbarrow or onto a piece of plywood for easy shovelling. Screenings are tossed onto the active compost heap to cook for another year . This device not only gives you the nicest textured compost for your garden, but will likely be the envy of the neighbourhood. It is also been great for sifting soil for new beds and peat for hypertufa projects.
Finally, you may wish to install wheels to it so you can get it back from garden buds whenever you need it!!!
With the lovely sieved compost, ten pound onions will be the norm next year :~)