How do I find the Commander for a TPU unit? Is there a site that lists this information?

Ask career counselor if they worth their weight in gold they know (if that's their area of responsibility) or if you can call unit (good luck finding numbers at time). Might have to ask career counselor to get number of another career counselor in that area to get unit POC, if you out of state.

If your not in the local area of a unit you can contact the ARCD BN at http://stayarmyreserve.army.mil/region_contact.htm

Are you looking for a unit in particular? You can use the RallyPoint search tool to see if someone in that unit can connect you.
https://www.rallypoint.com/search