Remove Old Computer Accounts

I am working on a large Windows 2003 Active Directory Domain, over the years computer accounts have been added but never deleted. ADUC shows over 2000 but we know there is no more than 1500 max.
Does anybody have a query that can be ran on the Computers OU of ADUC that will show all the computers that haven’t accessed the network in the last 3 months or more. After all if they haven’t been on the network for 3 months they are probably no longer in existance.