The screws that I use are called Confirmat screws and the size I use for this application is M7 x 70mm. You can purchase them many places, but I get mine from Quickscrews and the part number is 5361C. You also need a special stepped drill bit to drill out for the screws beforehand; they’re so large and have a blunt point, that you have to use the pilot bit or they won’t work. They’re meant for holding plywood together and are very strong.
The connector bolts I get from Hafele, but I think there are other sources. The part number for the Connector Sleeve is 267.01.715 and the mating screw is 022.34.157
Hope this helps…