Downgrade ios6.1.3 to 6.1.2 for jailbreak

Hi i am trying to jailbreak a friends 16gb iphone 4,
Its currently operating ios6.1.3.
Im aware that you cant jailbreak 6.1.3, so i am attempting downgrade to 6.1.2, however i am having an issue creating or finding SHSH blons for redsn0w to complete downgrade,
Any assistance would be appreciated

Thanks, C