you might have to buy a bit more than 10 meters
I only need 20 meters, but could get 50 if I manage to find a source. But if I'm going to pay the kind of price someone like Eland would charge then there are better and cheaper options for my application.
If the cable is made with natural rubber (which I don't think is common any more) then the strands are tinned to protect them from the vulcanising process. Modern rubber cables tend to be butyl rubber or even silicone so it's no longer a necessary part of the cable manufacturing and therefore less common. Why are you after tinned? Corrosion resistance at the terminations? It may be better to solve the problem another way.
As themadhippy points out rubber flex with tinned conductors is still available, just somewhat specialist. Have you looked at places like RS, Farnell and CPC? You'll have more luck there than with B&Q who probably won't even know if it's tinned or not.
The reason I'm looking for it is because it is (was) a cheap way to get tinned multi core cable - probably the cheapest in fact. I think I paid £12 for the 10m rolls in B&Q. That was five years ago. Why do I want tinned strands? It's for a marine application, where tinned strands are considered good practice. Interesting about natural rubber and corrosion from vulkanisation, did not know this. Pretty sure the stuff I got was butyl rubber or possibly neoprene though. You know, the usual H07RN-F type cable. Common as anything. I used it to replace the cables on stage lighting fixtures which came with short, stiff and not very heat resistant PVC cables. Still look like new today, despite the rigours of the road. I'm sure I can find many good alternatives at one of the big electronics suppliers, but these will surely have a price which makes them uninteresting.
Edit: Added picture of Helukabel H07RN-F, listed as "product withdrawn from sale" on TME. None of the 113 H07RN-F cables in their current catalogue have tinned strands.