Ran into the same problem on my old 200.
No Lexus or Toyota will not sell the bushes spare so you cannot replace with OEM unless you buy the whole hub or control arm on the front.
As linked above, bushes are available on the net. I bought some bushes, but then I'm lucky as I have a mate who runs a garage so we went there on a Sunday as you need acess to a ramp and bush press.
I can see why Lexus/Toyota don't want to change just the bushes as it's a bit of a pain of a job and takes an hour or two depending on how easy those bushes come out and go back in. It's so much easier, less labour and more expensive to replace the whole hub or control arms, that's why dealers do that.