Dave's comments and analysis are well taken. But in reading them and thinking more about this question I had some more thoughts. One thought was that really the demand for uncompensated instruments of this sort (roughly "euponium-ish") has historically been a Germanic/Czech-ish/Russian/Polish/etc. one. And they do have quite decent instruments. Whether any of those are at the quality level being discussed here, I have no idea. However, ...
There is an instrument of such a level of quality, I think, and that's the Miraphone Starlight. You can get it (discounted) for a bit under $10,000. So now you're going to say "But that's not a euphonium!" Really? Why not? Well, it's pitched too low. Is it? Too low, perhaps for the sort of facility real professionals are looking for in what they think of as euphonium performances (though in that case you do really need to catch a Baadsvik performance). But if it's really the high end of the range that's the issue, then what's the attraction of the uncompensated vs. the compensated horn at all -- since you're spending most of your time playing on just three (or two) valves? If what you're really concerned about is playing most of the time out of the range where four or five valves give you any advantage, then who cares how the extra one or two valves work? So stick with the compensating horns. Otherwise, rethink what may be some ways of thinking about things and see the Starlight (and similar horns) as large bore uncompensated euphoniums.
Similarly (or perhaps even more so) for small F tubas, although those seem to be notoriously difficult to produce with good intonation, no matter how much you're willing to spend.
I guess that if I were a professional euphonium player, I would look at the repertoire facing me, look at what a 3+1 compensator gives me, look at what a comparable quality 4- or 5-valve non-compensator gives me and say "Forget the non-compensating horn. It just doesn't provide any added value for my purposes." At least I'd say that unless I was from a culture where compensating instruments are the oddities and uncompensated ones are the norm.
Gary Merrill
Wessex EEb Bass tuba (DW 3XL or 2XL)
Mack Brass Compensating Euph (DE N106, Euph J, J9 euph)
Amati Oval Euph (DE 104, Euph J, J6 euph)
1924 Buescher 3-valve Eb tuba (with std US receiver), Kelly 25
Schiller American Heritage 7B clone bass trombone (DE LB K/K10/112/14 Lexan, Brass Ark MV50R)
1947 Olds "Standard" trombone (Olds #3)