You can get them from Global Car Parts
their website address is www.gcpdirect.com
They have got loads of products for the new shape IS
Check these out:
Standard Lexus IS mudflaps here
argento ice new lexus IS mudflaps
scratchproof stone chipping bumper protection for the new Lexus IS
new lexus IS250 or IS300 boot liners
They also do boot liners for the old IS, LS, GS, RX etc