1. if you're PS3 is brand new the 3000-4000 series (check serial code) it cant be downgraded because they come with 3.60 or higher firmware, sometimes the 2500 serie can be downgraded
2. yes, you should buy a used ps3 with 3.55 firmware/custom firmware on it, on a site like ebay, and if you bought a
3.55 ps3 it should ask you to update DONT do it,
3. use the search button
Regards