The sockets are made of porcelain, and come with a little metal piece attached to it for screws and such. (mounting bracket)
Go to a DIY shop and you should find them there, bracket included.
Only 1 or 2 euros each.
The bracket used to be L shaped but I bend them a bit, so I could screw them on the wood from the side.
The beer cans are connected together with aluminium tape and I made electric ground connection.
Like this :
I hope you can find them!
Good luck!