Try going to eBay and do a search on oxygen sensors I bought some for another car a few years ago that were universal 4 wire sensors you had to cut the plug off the old one and splice it onto the new one with heat srinks, but they are just as good as the ones you go to an auto parts and pay $60-$70 for I think when I bought those I paid $20. each. I haven't needed any since so I don't know if they are still available or not.

I really like the airhog panel filter in mine. Generic "civic" CAI kits/cone filters, off eBay are meant to splice in easy enough though. It's reputed that the K&N panel "does nothing" well the airhog felt like it woke it up. It's been said of the K&N panel filters though that they just make something that fits half the time and don't tune it for flow unless it's a performance model application or unless the owners clubs complain about it. I presume at least Fram knows what their paper filters flow, so make the airhogs flow better.

Edit: yes denso and NTK/NGK sensors are meant to do very nicely. (Same if you've got a Chryco product.)