Hi Lippi. Very good pictures. The bike looks to have had a lot of time and money spent, it looks a pleasure to ride.
The fork leg on the left side looks to be correct. The spindle should just fit in, matching the hole closely. If it is sloppy, then chance it is also the wrong leg. There is a vacant hole, facing forward, under the spindle. This takes a bolt and when this bolt is tightened, this clamps the spindle.
The nuts and bolts on your bike are not in general use these days, most common threads now are metric. BSA used a thread system which we refer to as Cycle Thread. BSA originally made bicycles, and this was the thread system they continued to use. This means any fastenings you need will have to come from specialist suppliers, not from your nearby auto store.
So you need the correct fork slider for the right side.
Part numbers to help you.
Right fork slider 67 5050.... The one you need
Left fork slider 67 5057.....The one I think you have, and looks correct.
Clamp Bolt 65 5295 This is missing. It is cycle thread, 26 threads per inch, 3/8"diameter shank, 1 3/8" long.
Here is a link to an online parts catalogue
https://www.google.com/search?q=Draganfly&oq=Draganfly&aqs=chrome..69i57.6048j0j1&sourceid=chrome&ie=UTF-8 You can search for any parts you need, and with the part numbers find your best deal.
The forum has a literature section. Have a look for BSA Service Sheet 212B. This shows the front brake and hub and how it all fits together.
Swarfy.