I play uilleann pipes mostly but I have been known to pick up my Chieftain low from time to time. Among pipers, there seems to be nothing as cool as a flat chanter (i.e. in a key below concert D - usually C#, C, B or Bb). I’ve seen C low whistles (Lunasa for instance) but not B or Bb. Do they exist? If so, who plays them? How do they sound?
colin goldie plays those big whistles, the only whistle that gives him trouble playing is the low low G or bass G, his arms are too short 
and he makes them anyway you like aswell http://www.overton.de/texte/pricelist.html
Alba has a Low Bb.
I own a Bernard Overton Bass A whistle. Now here is the thing. If you are having difficulty getting your fingers to make a low D spread, just play one of these HUGE bad boys and you will NEVER complain about a low D again!!!
overtons low A is great plays great haunting sounds
I spoke with Mike Burke about the possibility of making a low B natural, and he said he’d be willing to custom-make one for $300. There would be a bit of a wait as well. I’m sure it would be worth it though - his high B natural is a terrific instrument!
{Whistlesmiths take note:}
The larger “Baritone and Bass” keyless whistles can be made more comfortable for the player by incorporating much deeper playing holes. The Bassoon, Kortolt and Baroque Clarinets, as well as other low woodwinds, use this technique to draw the fingerhole spacing closer together.
Of course, there will be acoustic “short-commings” with deep toneholes, but adding a “pinched thumbhole” (Recorder) will allow for correcting flatness in the second register. I suggest adding a thickening “strip” over the tonehole area to increase depth(?)
NEVER say CAN’T!
Hornpiper - I’m curious: would you have Mike make the low B natural in aluminum or composite?