Extremely interesting feature, i love additions to the industrial/economy part of the game.
There are two things that i think could get some fine tuning, though:
1) the fact that only same-continent faction members will share a resource;
2) the lack of any form of compensation for the resource provider, especially a minor.
My suggestions:
1) there could be special convoys trading those resources between dinstant allies. These convoys should have a different panel and give to the player the chance to control them manually despite using automated normal convoys. Having periodic very important expeditions could be challenging, since you would give them the best possibile escort, even a fleet if necessary, and care about large-scale naval warfare/naval technology (not always vital or at least not for every country: with SU or GER often you can manage to have no convoys running at all for the first years of the war, depending on your strategy). The bonus given by the resource should have a sort of time-based expiration, forcing the country to obtain a new load or lose it and even be stackable up to a certain amount. Example: you trade coffee and get a +1% nightfighting bonus. With a once a month expedition you get +1%, but with weekly expetions you could get up to 4%. These imho opens up a intelligence war between the factions: spies should be able to report the frequency and route of the special convoys and enemies will try to intercept them (if they care, of course). Varying the timing could make harder to intercept, but would lower the impact of the resource on the economy/war.
2) I think that a major faction member would be interested in protecting and investing on the source of vital goods (a human player can do it without new features, but i'm not so sure if it would happen with the human playing as the minor country), so granting a strategic resource could be repayed with expeditionary forces to defend it or 0 cost production licences or even the control over a fraction of the major's IC to simulate weapons transfers. The minor should benefit from some faction leader's tech too: the rare materials production one in the case of Uranium, agricolture for coffee and so on: even if in the game the SR will have no quantity and just give a plain bonus, this would simulate the leader willing to maximize production. Of course the producer would benefit from the technology transfer, applying it to his whole production, getting something juicy for his own.
English in not my mother language, i hope that what i wrote is clear enough to be intelligible.