SHSH blob

Hello community

I have a question, and hope u guys have the info

I have a 4s currently in 6.0, the phone was never jailbroken before, reason why cydia never saved any shsh blobs, the Q is ... if there's a way to get the SHSH blob from an already installed IOS ?

since apple is signing 6.1.2 I could only download this version, but I really need 6.0 version for unlocking purpose

thanks in advance