Some articulated SFZ files from Japanese maker Unreal Instruments. Made for the Sforzando player, they might make an interesting translation, conversion exercise. I could not find any licensing terms, they include nice professional grade English and Japanese. user manuals. (Originally found in this Plogue list of paid and free instruments.)
Anyone with a Keytar would definitely want to check out the guitar sounds, there is a Standard and Metal version. Works fine with the free Sforzando player. These instruments may require more hardware than a Pi can supply, perhaps a multi gig Pi 4 could do.
Standard Guitar Sample (more tricky to play than guitar hero) uses some 2400 flac samples
Here is the control panel you get (instead of a GUI) on the free player, note the 13 CC channel assignments to panel controls, that looks easy to adapt to a headless translation scheme for some future Sfizz ?, the other 7 controls might be more tricky to manage.
Brief descriptions of the different Standard Guitar modes, articulation is done with designated non playing keyboard keys, except two modes where velocity changes the play style.
Wow good job playing the ModSynth_R1.sf2, it must be like reliving your first synthesizer knob twiddling experience. I imagine one could drop in more complex waveforms into that framework (if you can live with bloating the current 9.18k file size)
DecentSampler has about 16 free SFZ files, mostly novelty and toy instruments.
As seen in sforzando player:
Interestingly the Box harp has only Volume and Pan Controls.
While the Korg littleBits Synth Kit has 6 additional controls for Filter and Amp EG envelope. (makes the simple Square or Sawtooth a bit more interesting)
(Mandolin_Guitarophone_SFZ is the fattest of the ones I looked at: 730Mb compressed)