Nawa Drops have been rare on DSEC since it released.
The process of extracting them is used in DSEC missions to create RAM cartridges. (This statement applies to many toulan ore/enmatter - not just nawa).
Nawa is (since update 17.14) used in the Welding Wire blueprint.
DSEC-9 follows indoor mining rules... So if people were able to just fly to monria, go to dsec, drop a few probes and gobble up the nawa - they would be able to warp down to caly and make their welding wire with 0 need for import/export from Toulan.
Unless it's a happy coincidence; the rarity is by design.
The simple answer to anyone doing the crossover mission is to just fly to Toulan and mine there. If someone thinks a flight to Toulan is a big deal to progress the crossover... odds are they aren't completing it anyway. Don't sweat it.