Yep you're exactly right, you need the pedals off an IS300 as they're the only ones that came with them. However, they are impossible to find second hand, and new they cost a lot of money. I ended up getting mine from the US, cost about £65 including shipping. Only thing to note is that because they're off a LHD car the footrest is different so needed some modification to make it fit.
Thanks, aha didnt think of getting them from the US so guess i going to look into that then however i know alot of Altezza's came with them as standard think is only the basic Altezza that didnt come with them even that is hard to get hold of :( dont really wanna know how much new IS300 ones costs from lexus !