The problem is exactly like @olf nails it; usually having kernel sources is not the glitch but the proprietary modules is. There are ways around it, one can write wrappers for the proprietary bits and hence get as recent kernel as one desires but it is quite tedious and creates a maintanance hell. (but yes, doable if you desperately need a once-off solution) If you decide to go that way, be prepared to write quite a lot of support code against glibc...