Hi man,
I am no pro on all the different types so I am not much help there.
You can buy intakes from a lot of different places, including ebay. But If you want top notch service and company rep try Stillen. They sell a handfull of different kits. You may pay a little more that you would off ebay, but you cant beat their service record and reputation.
http://www.stillen.com/browse....LTIMA
I think your local auto parts shops can special order some. I know Autozone and Pepboys can special order the K&N sets, not sure how good their pricing will be tho.
But check out stillen, they sell a lot of other good add ons and mods too.