Hi Miniac, first may i say welcome to the club!
Ok, you are pretty limited as far as replacing the stock IS200 airfilter goes, TRD does one but it is basicly the original filter that has been dyed red and they retail at around £88!! (in my opinion not worth it) I also belive a company called trust does a foam filter but the filtering capability isnt very good, cost £????
I havent seen any commercial offerings of an induction kit, ( plenty for the IS300) there are a few homemade ones which i have seen in pics.
For the HKS you could try www.tdi-plc.com they are a lexus tuner, but im sure that there are plenty of other places selling the exhaust best thing to do is get one of the tuning mags and look thru the adverts.
hope this helps
rob.