Papuan Citron, would that be wild or cultivated ?(semi-cultivated?)
Similar question about C. hystrix and C. macroperta also listed in the database.
If cultivated may turn up in markets, which would be easier to collect from than travelling to village gardens.

Yes, I have the same questions.

It seems that markets is not a great tradition there.
Only very little and poor market places. Mainly selling betel nuts and lime (not the plant).

I had a look at the blog about the trip to Goodenough Is,
http://helenasadventuresintropicalpng.files.wordpress.com/2013/02/png-goodenough-trobes-fergusson-028_resized_1.jpg
Looks like ladies are selling varieties of taro, yam, sweet potato, chili pepper, sprouted coconut( called Angel Fruit, great to eat ). No greens but you might get pit pit, sweet leaf, rungia etc. also plaintain bananas
Looks much like the stalls PNG ladies sell from in Cairns QLD.
In larger towns maybe more variety ??

Yes, in Alotau there is a true market.