I actually tried KYB first - but didn't find anything. Doesn't mean there is nothing to find, just maybe I'm not so good at looking.
However - I did find this site - http://www.japan-parts.eu/ - which allows VIN lookup for Lexus, and then gives diagrams of subsystems from which you can get part numbers. So I got the numbers for my front suspension, and then looked these numbers up on a US parts supplier - http://www.lexuspartsnow.com/ - and found them. According to the http://www.lexuspartsnow.com/ site the parts have been succeeded by new parts, but either way they can supply the old or the updated parts. The two replacement parts (excluding shipping / import duties) will cost in total a shade under $400 (i.e. £260 or so) - which is astonishing compared to the Lexus 'standard UK' price of £311 each. Even allowing for costly shipping and duties, looks like the US route is massively cheaper than buying same parts in UK.
However, if it is possible to get existing shocks refurbished, that would be even better value solution I think. So do post results of your trip to suspension shop tomorrow - will be very interested to hear how you get on.