The tweeter has it's own part number and is replaceable at reasonable cost for the drivers in the R range. This is likely to be the case for your speakers. The parts will be available from any authorised KEF shop and, possibly, from KEF via the internet but I have only bought replacement parts from shops in the past. KEF have been clamping down a bit on people buying their drivers for DIY projects recently (they tend to have better value and performance compared to those readily available to DIYers) but since you are genuinely after a replacement part and possess the speakers and serial number there should be no issues.
