Prefilter is item #26 on this diagram:
http://www.peachparts.com/shopforum/attachment.php?attachmentid=39586&d=1166878138
It is not an inline filter typically found on the older models but is a molded plastic piece which fits into the filter housing. You need to buy the o-ring separately (item #29) and it MUST be renewed each time you replace the filter.
The parts you need are OEM only and commonly available at any dealership and even if they have to order them they can get them in a day or two, faster than having them shipped mailorder. I'd suggest you print out this diagram, go to the parts counter and get what you need there.