This is an interesting topic and perhaps those more knowledgeable than me will be able to answer with more authority. However…
There are some out there, look here for an example:
I, personally, dont think you can go into it thinking it will be just a lower volume version of a bigger amp. There just isn’t enough voltage to make the tube do what it’s good at. I have a number of tube pedals that try to simulate that preamp stage, but it’s just never the same.
That said… This could be really cool. Another option would be to find a tube that works best at low voltages.
Some other resources:
Here is a promising one in a kit form:
And another thread with tons of links to check out: