I assume you don't have a strong fleet yet (80+ ships with decent armaments) Nori is 'okayish' on 1-6, as in the drop rate isn't terrible and the only node that is trouble is the air node - which you can easily counter with a seaplane fighter filled CL + AA cut in DD (but you might not have either of those, sadly).

Tea is also decent on 1-6 but you'd have to choose which one to focus on (Nori or Tea) before overfarming kicks in; 2-3 is what should be easy enough for your level but the drop rates are pretty bad.

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3-5 is probably the best map to farm at currently, with decent passing rate to the boss (about 70~%) you have a chance to not only get tea (node F) but umeboshi as well (boss node).
Only problem is the resource cost but when you compare it to other maps in terms of runs it isn't so bad thanks to double food drop chance.

I've never bothered with 2-4 because it's too much RNG, I prefer reliability such as 1-5 1-4 for rice and umeboshi, 2-5 5-4 1-6 for nori and 3-5 and somewhat 4-2 for tea.
Also didn't switch any maps much at all until only I didn't get any food from the map 5 runs in a row, which is probably when overfarming kicked in.