A while back, I went to a pedal event at Q Division Studios in MA and the guy from EAE had built little pheadphone amps so people could test pedals out right next to each other without overlapping noise. He said they were still working on optimizing the design, but I haven't seen anything on it since.
HOWEVER, OBNE has their little utility series, which is pretty cool: https://www.oldbloodnoise.com/pedals/headphone-amp
And then there's... what? I guess the Line6 Pocket Pod? The little Dano mini-amp? I have no idea how well those take pedals...