The Britpart ones are the alloy core/plastic end-cap type which are common enough in the motor industry.
Bearmach sell both types with the alloy/plastic ones also being about £100 and the brass/copper ones about £170.
Check out your local motor-factors to see what they can supply.
Getting your existing one re-cored used to be a valid option but I have found that this now costs just about as much as a new (copper/brass) rad plus the fact you have no rad for a few days so there seems to be little/no benefit.