In my case I needed to search by MAC address to find my phantom machine to clear the pxe advertisement because the computer had a different name. It took a while to figure out how to add an item to a collection by mac address, so here's how:
Right click the collection, select Properties
Select the "Membership Rules" tab
Click the orange silo button to add a Query Rule
Give this query a name
Select "System Resource" and click "Edit Query Statement"
Select the "Criteria" tab and click the yellow * button
Click the "Select..." button
For Attribute class select "System Resource"
For Attribute class select "MAC Address"
Click OK. "Operator" should already be "is equal to"
For "Value" enter your MAC Address, include the colons
Click OK, OK, OK, OK to get out of the wizard.
Right click the collection, "Update Collection Membership" and Refresh
Now you should be able to "Clear Last PXE Advertisement" and redeploy the OS to it. In the future you can just Update Collection Membership and it'll find the machine no matter what it's name is.