I don't know if you'd be willing to sacrifice one of your programmable side buttons to keyboard lock but I find it very convenient. My right key locks the keyboard (since I'm a lefty phone user I just instinctively tap it as I slide my phone into my pocket).
Sorry I can't help you with a keyboard lock shortcut...I'm a little behind you OS version-wise.
Posted from my CrackBerry at wapforums.crackberry.com
I have the same rig you do. If you haven't deleted it, there is a padlock icon to lock the keyboard. After you lock it, tap a button and you are prompted to press * and then the green phone button to unlock.