The Google Developers have released Jelly Bean Factory images for a number of Nexus devices, including the Nexus 7 and more. They have included versions for several different varieties of Galaxy Nexus devices, although there are some absent, like the Korean and Sprint versions of the Nexus S, as well as the Verizon G-Nex. Here's a list of what is available,
  • Nexus S (soju): Android 4.1.1 (JRO03E)
  • Nexus S (sojua): Android 4.1.1 (JRO03E)
  • Galaxy Nexus (yakju): Android 4.1.1 (JRO03C)
  • Galaxy Nexus (takju): Android 4.1.1 (JRO03C)
  • Nexus 7 (nakasi): Android 4.1.1 (JRO03D)

It's interesting to see that most of the CDMA versions of devices take longer for these releases. Anyone care to speculate why that might be?

Source: NexusTablets.net via Google Developers