No, I don't know of one, although I've been thinking of starting one. I have some recommendations, though, in case they're helpful.

One Pi's are very small and very inexpensive, and are plenty efficient. The One Pi-plus-sub arrangement is essentially the same thing Doc Bottlehead has been recommending as his "Climax" system (except you would only have to build the sub if you bought the One Pi's ready-built).

I like the Two Pi's, which are small enough to suit my living room. Wayne recommends the Thermionic Series Three Pi's, which are smallish by horn standards but big by bookshelf standards.

There are some JBL studio monitors with horn tweeters that are very small and around $400 a pair that look like a pretty good option (but look to me as being pretty similar to the One Pi's again).

The Fostex BK16 horn is pretty small and is supposed to sound great, but you'd have the usual Fostex problem of having a really narrow sweet spot. I found the plans on a German horn site. I could forward them to you if you want.

And the Bottlehead Straight-8's are pretty small (tall and narrow), and are a pretty hilarious piece of engineering.

Those are the ones I can think of off the top of my head. Feels kind of weird name-checking non-Pi speakers here, but the Pi's come off pretty well on the cost/value ratio, so it's probably cool. Wayne doesn't seem to be the type of guy to mind at all, anyway.

-uW