The TFCs (Turkish Food Centres) : there are only 2 actual TFCs
http://www.tfcsupermarkets.com/branches.html
They are: i) in Lewisham High St, ii) large supermarket mentioned above on Bromley Rd opposite bus garage (the rest are in North London + Croydon).
However, there are other excellent Turkish food stores. The best one I know is on Catford Hill : it has a great range of food and fabulous bread ... and is easy to stagger over the road to the 185 bus stop with your bags after a shop. The one on Forest Hill Road - and the Sydenham Rd one mentioned above - are also good, but smaller, and don't have gorgeous fresh bread and pastry counters (though it is a year or so since went to Sydenham one so that could have changed).