There is a chart across a wide range of temperatures of thermal conductivity of selected metals in my copy of the CRC Handbook of Chemistry and Physics, but it is only for elemental metals, so while it includes iron, it does not include stainless steel.
Edited:
That chart referenced "NSRDS-NBS 8", which can be found here:
http://www.nist.gov/data/nsrds/NSRDS-NBS-8.pdfWhile that report does not include stainless steel, it does have some very nice graphs showing how thermal conductivity of metals vary with temperature, and in a pinch, it looks like you could use the slope from that graph to estimate the variance along a reasonable range of temperatures, as above cryogenic temperatures, the graph appears rather linear. Even if you cannot derive useful information from the data, it is good reading to understand how the data was collected, and where the variance comes from.
Although I don't have access to this, you may be able to find at a better library:
"New measurements on thermal conductivity reference materials" by Powell, R. W., and Tye, R. P, in the International Journal of HEat and Mass Transfer, Volume 10, Issue 5, May 1967, Pages 581-596
It looks like that may have what you want.
This document includes a range of temperatures studied for 304L stainless too:
http://symp15.nist.gov/pdf/p713.pdf