Apple has released iOS 6 firmware for iPad Mini and iPad 4, which is available now for download directly via official links embedded below.
iOS firmware build 10A406, iPad 2,5 is for iPad Mini whereas iPad3,4 build 10A407 is for iPad 4.
Download iOS 6 Build 10A406 for iPad Mini
Download iOS 6 Build 10A407 for iPad 4
See also:
iPad Mini Specs
iPad Mini Media Event KeyNote Video