Where to get protective cups for under spikes?

I had great success with fender washers from HD, glued together using JB Weld, painted flat black. Fender washers are easily identifiable by their smaller than usual hole. You'll need as many that your spikes will fit into without the points touching the floor, and then one more for good luck.

VTI sells packs of 4 for $24.

I agree with Davemitchell, use quarters. First I used a 3/16" drill bit to put a small crater in each of eight quarters (for the spike point to ride in). I then glued the quarters to a piece of leather. After cutting out the quarters/ leather pieces I placed them under the spikes. The leather protects the floor from scratching and the small crater keeps the spike in place for final positioning tweaks.

Acousticsounds.com

The Lovan Footer is a great product; available in black or chrome