This Might Not Exist, Any reasonably priced, smaller speakers with 100db Sensitivity?

Nothing wrong with building a system around a particular amp, especially if there is a specific tube you like the sound of. Low powered tube amps have limitations, as has been stated above, with speaker choices. More often than not, they require bigger boxes. I write this as I’m listening to a type 45 amp, driving a pair of 6’ tall double backloaded horns using a full range driver. Not to everyone’s taste, but I find the listening experts be quite enjoyable. 
 

Good luck with your search!

 I'll also add that there is another emerging category--the high power tube amp aimed at the 90dB sensitiveity speakers.

"Emerging"?  Hardly.

As has been mentioned, you couldn’t go too far wrong with a pair of used Klipsch Heresey’s or even the RP 600. Another Avenue would be to invest $59 in a pair of Lii audio F6’s and put them in an open baffle. I did this and used it with my flea tube amps and was sufficiently impressed that I went on to buy a couple other Lii speakers For more ambitious projects. Open baffle works really nicely with subwoofers in my opinion because you get the open air sound without sacrificing the deep base as you normally would have to. furthermore, I like the fact that you can use them for range without any crossover which keeps the efficiency high and also better preserves the integrity of the signal. to go on this level it seems like you have to get in to the large cabinets with folding horns or even a Voigt pipe design. These speakers come with their own demands on space, weight, and aesthetics.

Zu Audio recently announced the small Method bookshelf speaker.  94 dB sensitivity.

https://www.zuaudio.com/loudspeakers/p/mb1

Tekton is a good choice.call him tell Eric what you want he can heip.enjoy the search