Welcome to the Forum.
First it is important to know if you have a Jig Saw or a Scroll Saw. There is a difference even though many people use the names as the same tool. The picture below is a Shopsmith Jig Saw. I happens to be a Greenie from 1957 that I restored. Later they were painted in the Goldie paint scheme in the early 1960's. After that they were painted gray with a black arm.
If this is what you have than the Table Insert is Part Number 502254 which is no longer available new from Shopsmith. It will have to be found used.
If you have a Scroll Saw like the one shown in the picture below or the earlier gray one (bottom picture), you will need part number 515196 which is no longer available new from Shopsmith. The newer Scroll Saws, as seen in the picture below, have a slot cut in the table and no longer have a need for an insert.
A gray Scroll Saw table is shown below and you can see the table insert it uses.
Both the Gray and Teal Scroll Saws have had versions made mounted on a stand and for Mark Mounting.
Mark V completely upgraded to Mark 7
Mark V 520
All SPT's & 2 Power Stations
Model 10ER S/N R64000 first one I restored on bench w/ metal ends & retractable casters. Has Speed Changer, Model 4E Jointer, Jig Saw with lamp, a complete set of original accessories & much more.
Model 10E S/N 1077 oldest one I have restored. On bench w/ metal ends & retractable casters.