I don't think you can, unless you get a court-issued warrant or hire a PI. There are all kinds of privacy issues involved in trying to do something like that, at least when trying to through official channels.
You could try simply telling the collection company that they are calling a number that is no longer used by that person. You are not Jennifer Watson. Continual, repeated collection calls after they are made aware of this fact could constitute as harassment, and you may want to bring that issue to somebody who can provide proper legal counsel.