Im sure they could find them. but honestly im a little confused how they went missing in the first place. I would get in your trunk with a flashlight and find them, shouldn't be to difficult. As for the rear deck speakers, go ahead and replace them, especially if your not going to include a subwoofer. A good pair of 6x9's will give you much better bass output then just a pair of 5 1/2's upfront. I have always been a huge fan of infinity's. I run a par of component 6.5s upfront and a pair of 6x9's in the deck and a pair of 12's in the trunk. Im a huge fan of audio quality and I love the clarity of my system. Good speakers at a good price, choose infinity. Let me know if you need any more help!