Have you considered grinding the all-thread to a point. I needed one spike for a speaker and instead of buying a set I bought a bolt with same thread pattern at Loews. After grinding it to a point it worked like the original as far as I could tell. You will have a problem though if you want to move the rack to a spot where spikes aren't desired. Good luck.
Source for tapped spike for flexy rack
I have just finalized the design of a "flexy" style rack utilizing 3/4-10 all-thread rod and plywood shelving. All hardware is available at my local industrial supplier with the exception of spikes or cones for the rack's feet. Does anybody have a source for brass or steel spikes which are available tapped for a 3/4-10 thread? I've found a couple online, like Michael Green Audio, but was hoping to spend less on four spikes than the cost of the rack itself. Thanks for any help.