I don't know any vendor that still makes those old square type rubber feet. Every old rig that I've owned, especially the heavy ones, with missing feet, squashed feet, damaged feet, etc. were replaced with 4 (or whatever quantity) round rubber feet. Square rubber feet with adhesive type backing are still around in many sizes, but they have to tendency to fall off or creep especially if you try to drag the equipment across a surface. You also need "manly" type feet, those that can take the weight and stress for long periods of time.
Here's one for the enormous price of $.89 each:
http://www.starcase.com/detail.aspx?ID=36