Where can I find the floor gasket that covers the steering column and clutch floor holes in my 63 F100

 

Is this the gasket you are looking for?

Steering Column Gasket

 

This is the gasket shown in the Ford truck parts catalog (see pic), but Mac's has the wrong alternate part number listed.

The original part number for 1961/64: C1TB-8101738-A

 

The reproductions are either incorrect or there was more than one variation and only one variation is produced.
I made a drawing showing the difference between a reproduction that I purchased and what I actually needed. The reproduction places the hole lower and to the left of the correct location for that hole. This leaves a gap below the column and eventually the rubber tears.
You can use the screw holes at the perimeter to determine where your column sits and then if the reproduction rubber will work for you. If the repro will not work, then the only option is to make your own.