Looking at a boat on a myco trailer, 6 lugs, is this a common six lug? I need to pick up a spare if deal goes thru

Its my understanding yes,, if it has Kodiak brakes then definitely yes.

older trailer (94), just your typical surge brakes

myco generally uses torsion axles with dexter hubs. http://www.dexteraxle.com/home_ or call myco and speak to Will (i think) in parts. I have totally gone through mine and they are great to work with.