A lot of people here use
imgur - this forum automatically recognizes the link and embeds the picture (unless you put it in spoiler tags, as a courtesy to mobile users on the regular forum threads).
Ok, that screenshot just shows the synthesis menu for explosives - and as you don't have any materials, you can't synthesize additional ammo for your seeker missiles. So, if you run out of ammo, you need to buy it from a station that offers restock (not all do). But this has nothing to do with whether the missiles would show up (or not) in the main HUD when deploying hardpoints. Even without ammo, they would show up - with the ammo counter at "0/0".
Can you add a screenshot of your main HUD (view out of the front window) with your weapons deployed, but not showing up?