Thing this the IS wasn't massively successful in 1 country. It enjoyed good sales across Europe, Australia and the US and as the Toyota altezza in Japan. But it was still outsold everywhere in the world by 3 series BMW's, Audi A4's and C class Mercedes Benz.
US is where the most were sold and a lot of people on here talk about getting parts from the US.
Just remember, genuine Lexus parts are engineered to last longer so they will be more expensive. My IS is 11 years old, 92k on the clock and I'm still on all original shock absorbers, springs, wheel bearings and exhaust. Tell me another car that's 11 years old with the factory fitted exhaust and suspension still working perfectly?
You get what you pay for..... :)