A trick I have used when searching for other people, goes around the houses a bit but worth the effort.

Contact reputable contractors in your area or close to. Phone them up tell them you are doing research or survey regarding the employment of African tradesmen ie how many they employ are they employed directly or as subcontractors(it's the subcontractors you really want-but either will do) You will need to ask a series of prepared questions. Then ask for their contact details for further info failing or when you would be able to contact them at the company office/depot.

If you get their personal phone numbers then phone them up, if not turn up at office or depot when you know they will be available.

The last time I tried this the company(Housing Association contractors) arranged for me to interview their employee I turned up asked my made up questions and then got their number to do some work.

The guy was great, did the job and still have his number and gained him lots of work over the years (unfortunately here in the midlands so not worth passing on). As it was the lady who needed the work was retired so not sure if that is why he didn't make a pass at her. And I guess he didn't make a pass at me since one of the first questions on my fake interview was are you married/single/co-hab.

The first time I tried it was for an electrician The brother was a subcontractor who employed pure white boys, who did a good job but kinda defeated the purpose, although the person using him took solace knowing that he was the one earning the money, that was in Sheffield.

Like I said it goes around the houses but you can gain valuble info. Many brothers worth employing already work for or subcontract with established fims.