I'd go with what Simon has said. I buy parts from rockauto as even with delivery it's cheaper than main dealer parts, some parts can take from 3 days to a week to arrive, or I buy parts from lexus birmingham as Simon said, they do give a good discount. An example, I was looking at lower ball joints for an ls430 at Lexuspartsdirect, their price is over £80, lexus birmingham sell them for £52 All in and rockauto was around £30 for the same part, front pads and discs from Lexus birmingham cost me £142 all in.
But Lexuspartsdirect do give discount on some parts.