As soon as you have a good slave, you should do A Word In Your Ear in the Plains whenever available, as it's easy to ace with a quality slave, gives lots of supplies, doesn't require many slavers and is repeatable on a critical.I have been playing on normal difficulty and the lack of supplies has been killing me, does anyone have any advice? I have been trying to farm the great plains, but it does not seem to be enough.
The emissary call is also a good one. Another way of getting supply routes is critting Tavern Takeover (exploration version only).