If you were a "first time trial" person, AV would be unlocked as part of the trial license.
Since you're an existing customer, with a license key, all you need to do is to get in touch with your regional LANDesk sales folks, and let them know you'd like to have a trial of AV. They can then add a trial license (for X number of days, that's an individiual agreement) to your existing license, you just reactivate your Core, and voila - you get to look at LDAV.
It's not a lot of work in that regard (you just need to know "how").
So - a phone call + a reactivation is pretty much all it takes .
LANDesk EMEA Technical Lead