There is in fact a delightful Fritz fandom on tumblr, full of less than historically accurate fanart and cosplaying and whatnot, and I do occasionally link to things there. In addition to the "Keeping up with the Hohenzollerns" comics that selenak linked to (there are others, just click around), these are some of my favorites:

Be a shame if something happened to it
Oblique attack tactics (Oh, iberiandoctor, you know about the epic rap battle involving Fritz, right?)
Bavarian Succession
Military defeats are homophobic.
Orgasm poem
Whoooo's a good girl?
Gru's plan meme
Should you fight them: Prussian monarch edition (Selena points out this is not really fair to F3)
Fritz/Fredersdorf meeting
Looking good in uniform.
The musical
Fritz, are u ok?
Katte ghost
Drunk Fritz episode
Slut
My OT3 in college (Because I'm a sucker for a modern AU.)

Oh, selenak, remember your icon post where you said there was only one color portrait of Hans Hermann online? Aside from the plaque (which I think would make a good icon), while going through my looong list of tumblr links, I found a couple more that purport to be Katte (though this tumblr user mixes up the many Keiths, so I don't give these 100% credibility unless you recognize any of them) and also some of the Katte family members:

- Katte (This one I recognize in black-and-white, so the color version is probably correct.)
- Katte and sister concert
- Dad and (maternal) Grandpa
- Dad and Mom

Hans Heinrich does have a somewhat recognizable face that looks similar to the one in the most famous portrait of him, so those might actually be him.