Don't give up! It took me three days to get the Ryuryu while both Bernice and Dorothy dropped within first three-five runs. So you too will see the completion eventually! Hopefully...

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Gotten Vincent within day's worth of stamina too. All it took for last drop to appear was bringing different team

Really, if map gets you mostly the same drop, try clearing it with different team composition. Wiki-goers have half-serious theory that Aigis's RNG uses you team lineup as a seed in some way, so who knows, it might help