Hi,
I am not aware of any existing spec released by Altera, however you can buy the HSMC connectors from Samtec and make your own expansion cards for the new dev kits. You can collect the necessary info from these places:
For pinout/signal names on the CIII kit, see the files in Schematic folder you get when you install the software which comes on the CD in the box.
For mechanical specs, see the manufacturer's catalog pages:
http://www.samtec.com/custom_products/highlight/asp-122952-01.asp (
http://www.samtec.com/custom_products/highlight/asp-122952-01.asp)
http://www.samtec.com/custom_products/highlight/asp-122953-01.asp (
http://www.samtec.com/custom_products/highlight/asp-122953-01.asp)
For electrical specs, PCB libraries and other info, see the Samtec qth (
http://www.samtec.com/technical_specifications/overview.aspx?series=qth)/qsh (
http://www.samtec.com/technical_specifications/overview.aspx?series=qsh) series.