How does Kimimaro's Kekkei Genkai work? According to the wiki, 


  Shikotsumyaku (屍骨脈; Literally meaning "Dead Bone Pulse", Meaning (Viz) "Corpse Bone Chain") is the kekkei genkai of the extinct Kaguya clan, which gave them the ability to  manipulate their own skeletal structure (their osteoblasts and osteoclasts). By infusing their calcium with chakra, they could manipulate the growth and properties of  their bones to their liking.


Now, surely that means that they're working with the base amount of calcium (and other minerals) in their body. The fact that they're able to grow their own bones seems to indicate that they are able to get the calcium (and other minerals) out of their nearby surrounding in some manner. Is this corroborated in the manga?

The last part is just my own speculation. Please do correct me if an alternate explanation exists.
Kimimoro's Kekkai Genkai isn't like Gaara's sand.  Gaara's sand can go underground, smash the rocks, and use the hardened minerals from the local rocks and incorporate them into his sand.  Kimimoro doesn't seem to do this at all, but rather his bones and chakra system is all internal.  

I think this is evidenced not by what he does but by what he doesn't do. In his battle with Gaara which is clearly his most pressing battle (since he dies in it) he transforms multiple times, he uses his spine whip, and does a number of other jitsu but never absorbs from his exterior surrounds while Gaara clearly does.