If the Kings are going to get an upgrade at the PF position in any way other than signing Antoine Walker (i.e. getting someone who could conceivably start over Kenny Thomas), it's going to have to come via trade. Here's an approximate ranking of the PFs in the league by category of availability:
Untouchable - not coming to the Kings, no way, no how, don't care who the Kings are offering (in no particular order):
Kevin Garnett, Dirk Nowitzki, Chris Bosh, Tim Duncan, Chris Webber, Dwight Howard, Emeka Okafor, Jermaine O'Neal, Amare Stoudamire
Basically untouchable - not coming to the Kings without trading Bibby, Peja or Miller (in no particular order):
Elton Brand, Antawn Jamison, Rasheed Wallace, Kenyon Martin, Tyson Chandler, Pau Gasol, Zach Randolph, Al Jefferson, Shareef Abdur-Rahim
Not untouchable, but the Kings don't have the pieces to get them - players that aren't crucial to another team, but for whatever reason they're not coming the Kings' way (in no particular order):
Udonis Haslem, Antonio McDyess, Donyell Marshall, Michael Sweetney, Robert Horry, Stromile Swift, Nene
Possibly available - players the Kings could conceivably, possibly, maybe get with the pieces at hand (in no particular order)
Antoine Walker, Drew Gooden, Kurt Thomas, Troy Murphy, Raef LaFrentz, Joe Smith, Matt Bonner, Carols Boozer, Reggie Evans, Antonio Davis, Nick Collison, Melvin Ely, Chris Anderson, Malik Rose, Zaza Pachulia, Keith Van Horn, Juwan Howard, Othella Harrington, Robert Traylor, Alan Henderson, Brian Cook, Eduardo Najera, Michael Ruffin, Maurice Taylor, Dale Davis, Scott Padgett, Danny Fortson, Kris Humphries, Anderson Vaerjao, Etan Thomas, Christian Laettner, Tom Gugliotta, Calvin Booth, Malik Allen, Slava Medvedenko, David West, Clarence Weatherspoon, Aaron Williams, Macej Lampe, Darko, Brandon Hunter, Bo Outlaw, Pape Sow, Sean Marks, Vin Baker, Michael Bradley, Michael Stewart, Torraye Braggs
I'm not really liking the Kings' options. Right now it's looking like Antoine Walker is the most likely and most realistic upgrade. I also like the idea of somehow plucking Kurt Thomas from the Suns, say for Kenny Thomas and a re-signed Maurice Evans.
But if there's a trade not involving the core, that's some slim pickins.