Tube amps known to have a low damping factor?

I would instead look at the output impedance ratio to the nominal impedance of the speakers the amp will drive. You want a ratio of at least 10 between nominal speaker impedance/amp output impedance. Anything less than this will usually cause a drop off in some portion of the frequency response, depending on the impedance curve of the speaker.

I plan to do that, but right now I'm just asking for a list.

CAT JL-2 has a DF of 10. Why do you want a low DF? I thought I high DF was desireable...