iro mark v for street, sh itamori peloton for track
the only ones i've been able to find are pretty cheap. i'll be racing with one on my front this season though. i mean, it certainly beats swapping out the axle, especially if you're dealing with sealed bearings.
I'm planning on using one of these. I use a set on my commuter bike, but the bolts are plastic and overall kinda flimsy. It'll keep a crackhead from making off with my front wheel, but I think I'll spend a couple dollars more and go with this one for the velodrome.
You could also find a local machine/engineering shop and ask them to mimic the skewered axle, only making it with threaded ends so you can bolt it on. But, if the Zipp axle is legal and strong I'd run with that and call it a day. I think I've seen people using those were I race, but I'm not certain.