Hey, have you build the specialist terminal for the armourer yet? Technically you don’t have to first but give it a shot if you haven’t already, could rejig something to happen.
Another quick fix is go through a blackhole with the mission active (polo can help you find one on the nexus) and then it will either point you to a Vy’keen armourer in a nearby system or you’ll get a red warp icon on the mission saying the armourer is impossibly far away and let you reset the mission. You can then go back home and reset the mission again if you’d prefer to find one closer to your home systems.
They’re not always necessarily in Vy’keen systems either, you can stumble across them on any old station, I found mine in a korvax system on my new playthrough, he was in the room beside the upgrade module sellers, chillin with a Gek.