So, this idea is a little crazy, but it's a missile annex. Missiles would generate much like the expansion points or boosts, but very slowly. Let's get into probable details.
So, for stage one of the missile annex, it would do absolutely nothing, just kind of sit there until upgraded to level 2. Once upgraded, it would start making Storm Missiles once per either 24-48 hours. It would have a capacity increase to 2 at level 3 and after that, a time decrease. At a higher level it could either;
A: Continue producing storm missiles at a faster rate/higher capacity.
B: Produce Skypiercer missiles at twice the time of a regular Storm missile.
If a missile annex is attacked maybe it could reset the time required to produce a missile?
Otherwise, if you aren't liking the idea so far, you could have missile armanents scattered around the map like the other caches. Possibly capturing Storm missiles or Skypiercers if you're lucky. This could give alliances something to fight over or a rush to arms and give losing alliances a new edge.
Thank you for your consideration. We just need an easier way to get these things. Not all players have a bottomless bank account, so even if the method of obtaining them is difficult, it is still possible.