Isn't the standard operating procedure "help civilians in exchange for the safety that the resources they collect provides"? Unless we're planning on helping civilians for no benefit (or worse) to us? They have things (goods and information) we want, and we can help them to get some of those things. The less they have to worry about the things we can protect them from, the more they can produce those things, and the more we can harvest from them. Sure, missing-nin have significant difficulties in providing the safety bit and it likely comes out "if you give me want you want now, you'll be safe from me for the moment," but ninja-civilian relationships seem to be all about safety from the deathworld in exchange for goods and services.
If the
canon images of Iron are anything to go on, we'll need winter gear and skills there as well.
Personally, I would expect missing-nin from Waterfall and Rice (or maybe just plain Sound Nin, considering Orochimaru) and, for those that can cross the bays, Earth, Hotspring, Frost, Lightning and even Snow.
One of the biggest things I'm seeing if we try for a civilian cover is lack of resources. If we have trouble gathering the resources in a plausible manner to cement a civilian cover, it makes it that much harder to sell. And if we have to use ninja abilities to make it, we're necessarily going to have to reach for relatively low hanging fruit as we don't have the skills to reach higher, so other ninjas looking for low hanging fruit will be our competition. If there was plentiful low hanging fruit in Iron, why do we think that "they don't have much that anyone wants" and that there's "not much in the way of natural resources or anything to attract outside attention"?