Hi Gazman,
I bought it from a Lexus dealer in the US, having emailed them previously to make sure they had one in stock. I guess you could try and see if a UK dealer can source a US part for you, or alternatively get one shipped - it is pretty light. Those customs guys will get you though as will the Post Office with their "handling fee" - how the heck do they get away with that anyway ...
You can probably find a third party bra in the UK, but the Lexus one has a nice embossed logo and it is well made I think. The part number is : PT21848040 - MASK, 1/2, RX. List price is $124.30 + tax.