Problem- Ship Building Materials

All I can tell you is that I've been buying ship building mats from cantina shipments for a long time. All my ships are max level and so will any new ships, I even splurged 60M on mods the moment they introduced mods for ship mats in the mod shop. Refresh cost for mod shop is surprisingly very reasonable.
And I'm still buying mods with ship building mats regularly so I'm pretty sure you will eventually reach this stage once you progress further in the game. And you should be able to afford more than 1 cantina shipment of ship building mats daily if you're refreshing cantina energy.