I'm not sure why the funds ended up as unclaimed, but if you have to have the buyer's information to claim the funds, here are some simple things you can do.
1) run a Google search on the buyer - you'll be surprised at what you can turn up. 2) send a letter to the buyer, at the last address you have, and put on the envelope, under your return address, "Address information requested." 3) check the Harris County clerk's office databases - there may be information in any of them that can help you locate the buyer http://www.cclerk.hctx.net/applications/websearch/ 4) check the Harris County Appraisal Distrist site http://www.hcad.org/Records/, or 5) the agent should be easy to find either on the Houston Association of Realtors site http://www.har.com/ or on the Texas Real Estate Commission site http://www.trec.state.tx.us/. Good luck!