A lot of talk and discussion about one particular dealer here, i'd be very surprised if you can't find another Lexus dealer in the US willing to help or maybe even an aftermarket parts supplier willing to source OEM parts and supply.
In the Toyota world there are quite a few of us who have been sourcing spares from the US for many years and there are nowadays a number of dealers willing to ship worldwide. The many online parts catalogues mean making sure you specify the correct part number at the time you order easy enough and the parts can often arrive in just over a week (if in stock). As for tax, well sometimes you win, sometimes you loose you just need to consider this in the overall price you are quoted.