I would go straight to the place that you saw it advertised, they will certainly have the full details for invoicing purposes, but may be reluctant to hand them over to you, there are two alternatives, make a complaint to trading standars they might not be able to help, but also might have had complaints about this person in the past or ongoing so may be glad for your input, if this doesn't work you can purchase a subscription to www.192.com which allows you to do a reverse number look up... might be pricey but it depends how out of pocket you already are, or if he's a registered company which seems unlikely the company details will be available through companies house
http://www.companieshouse.gov.uk/
or how about getting one of your mates to call him and get him round to quote on a job see if he can get address details out of him.