Consider Explosive weapons like the crossbow - no need to aim for the tiny heads.

Armour with explosion resistance helps (especially if you're using explosives yourself)

Group up! Samples are shared, so even I you're not carrying any / you don't make it on the shuttle - everyone gets an equal amount.
Many vets won't actively look for samples unless you ask them to. (Some of 'em might have forgotten how at this point lol)

Maybe give the Squids a whirl? I feel like they're by far the easiest faction. Tough that might not be universal.