thanks for your answer!
I already got the genetic map provided by USCS database with STS markers.
But my issue remains the same: the density of markers of the available genetic maps (the USCS one or HapMap II one) is much lower than the density of my SNP set. For example I have 4054 SNPs between the 2 STS markers above (in your comment).
Therefore I don't know how to attribute to each SNPs of my set a position in cM without doing a very important approximation.
Anyway, what do you suggest? To use a rule of three approach to attribute a cM position to my collection's SNPs?