I asked a few folks a month or so ago for recommendations on a supplier. Jazz suggested Chai on ebay, he provided a good price and the cable chain arrived a couple of days ago. Its a 57mm internal size so larger than you might be looking for, it doesnt unclip bit for the size thats ok. I also purchased the following on ebay a while earlier and it does unclip.

UK Cable drag chain wire carrier 18*37mm R48 1000mm (40") with End Connector | eBay