The last one is the insert on edge but basically the insert is about 1/16th thick and has a tab on one end and a spring clip on the other. If I had a way to cut 1/16th plate steel I could cut out the insert then take a 10 inch metal cutting blade and cut the slot and the tab and spring clip would be easy to do.
Thanks for the great pictures. You can make your own out of 1/2" BB plywood. Use the metal one as your pattern. Cut out the plywood one 1/8" larger and attach the original insert upside down on the plywood blank with D/B tape. then with a flush cut ball bearing router bit,with the bearing following your old insert run around the outside to cut the shape of the new insert.
Then set up a rabetting bit and rabet the bottom edge all way around the depth of the lip on the edge of the opening leaving enough material on top to flush out the insert with the table.
When you drop in the new insert, if it is too thick such that the blade touches the bottom of the insert, install a smaller diam. blade. Raise that blade slowly while running to just barely cut thru the new insert enough to give clearance for the regular blade.
The set up for cutting thru the insert, is move the fence over the insert and clamp a block forward and aft of the blade setting down on the insert clamped to the fence, this will keep the insert from raising while cutting the new slot.
You might find some of those cheap cutting boards at the dollar store made of HDPE plastic to use too. What ever you do ,make up several at the same time to have on hand, you will thank yourself later.