Found it! Once you log into your force 10 account, scroll down to the bottom of the page. "Note: To see the full list of Supported Software downloads, please click here" Once you click the link you will be taken to a page with more links, and the uboot link is listed.
I have access to the support site and get the latest firmware for the 4810 - but the release note suggests I need new boot code too u-boot.1.2.0.5.bin - but that does not appear in the list of available downloads. Where can I can that from ?
Updating a 4810