Raid Mk3 is the easiest way for higher relic mats. I exclusively use Mk3 for Electriums, Zinbiddles and Impulse detector and Gyrda keypads. With a low income I would prioritise Gyrda pads until you have banked enough for a R9 requirement. The key is to build up personal raid performance and being in a guild where everyone is working toward these materials.
High performance in conquest hard mode also provides a more personal route if your guild struggles with raid or to add more even with a good raid performance. Tier 5 gives best Electriums and Tier 6-7 give best Zinbiddles and Aeromagnofiers.
Until you have a good economy in raid and conquest be selective on characters to raise above R5 and R7. Only take requirements or characters which return investment whilst your rewards are low. I only started taking attackers and tanks up which were not requirements when I had a generous supply through the raid.
If you need a limited amount, such as 1 R9 character for a journey guide unlock then crystals can supplement a low raid performance for a specific requirement. I got my first R8 using crystals when chasing JMK before we completed CPIT. And JMK improved my raid score to access more aeromagnifiers later on. The crystals is worth a meta ship like profundity, Levi or a GL. Which can help boost Crystal income. But not worth taking up a random character which may perform sufficiently at lower relics with good mod investment.
So there are no quick routes, but it progressively gets better as you advance through high end activities such as conquest and the raid.