Try here. Shipping isn't cheap but maybe you know somebody holidaying in the US? Shows how Lexus rips off it's UK customers!
Total cost of rear pair about $250 (£200 as I write) of which $90 is shipping. I owned an RV some years ago and parts from the States were a fraction of the UK cost....and the service was much superior!
https://www.carid.com/dorman/rear-brake-dust-shields-mpn-924-373.html?singleid=118829631&url=83981917
https://www.lexuspartsnow.com/oem-lexus-backing_plate.html?Make=Lexus&Model=RX330&Year=2004&Submodel=JPP&Filter=()
Try both, shipping costs can vary.
