(First post, wohoo)
First of all, the Marines have plenty of seastone since they even cover the down side of their Battleships with it so they can cross the calm belt. It's only rare for civillians.
Second of all, Lucci vs. Sir Crocodile. Since Lucci is Cipher Pol (basicly secret service as you know) he most likely would know about Crocs Water-Weakness. So Lucci would just have to make his hands wet and he could Shigan the hell out of him. (if Luffy was able to hit him back then, then Lucci who is like 5 times stronger and 20 times quicker than alabasta Luffy (he was even quicker than "normal" Enies Lobby Luffy) would so be able to do it too) He would not have to use is DF either, since he is so incredible fast.
And by the way I for one think that Lucci would be able to defeat crocodile even while fighting in the desert, since Soru and Geppou grant him incredible moving capabilitys (not to speak of Kamisori).
I also tend to believe that the World Government gathers any kind of information about any better-known pirate, like Governemnts do in the real world too (about criminals). And since Croc was even working with the government I would highly wonder if they had not a file with Crocs name on it and his weaknesses in it. Same goes for all the other Shichibukai at least.
Not to mention the Devil Fruit Research Stuff done by Vegapunk and the Devil Fruit Catalogs with Info about the Devil Fruit in it, it's highly possible that the Suna Suna no mi is listed in it too, along with its effects and weakness.
And on top of all that, it is my personal believe (and I dont expect anyone to agree with me on that one) that Roku-Ou-Gan would work on Croc even without Water, since Ruffys Bazooka during his first duel with Croc in the Desert kinda worked too, and since Roku-Ou-Gan goes beyond outer damage and has the same effect as "An impact dial going off in one's chest".
Third of all, I think that Mihawk is the only one of the shichibukai who has not a crew, since he is really something special (strongest swordfigher in the world) I would say that Kuma has something to do with somekind of church or something. Maybe he's somekind of saint to the church or so and I kinda doubt that he will ever battle the Straw Hats.