It's just another thing the developers forgot about. A bit like gold dust. There should have been a recipe but there isn't, so you have to use the alternative method of getting it. I doubt SE intended us to fight rank 95 mobs to get mats for a rank 42 tool.

Although it is interesting that the jester's cap seems to be the only vintage piece you can get by factions without having to synth an upgrade for it. They did that for a reason, why I don't know. Perhaps the recipe uses a material that isn't in the game yet so they stuck in the upgraded item too.