I came across a good few of flat-chanter - reed combinations so far but none produced a hard E. Does this exist here at all? (and I also categorize Narrow Ds as belonging to the “flat family”)
Every Wooff chanter I have ever played, and I have played a few , had a solid hard E.
Nearly all, if not all, of Joe Kennedy’s, including his Ds (which are not all narrow-bore) have had it as well. My D chanter is finicky about it, but will do it when the weather’s right. I tried a prototype Rowsome model of his and it also did it.
I don’t remember any chanter that didn’t do it, but there may have been one.
One of my Robbie Hughes D-chanters did and the other wasn’t as keen on it.
The Rogge B chanter I used to have had a solid hard E, as does the concert pitch Rogge chanter I have now.
My Gallagher B plays an off-the-knee hard E nicely.
Rogge B here, too, with hard E.
All Hunters, especially NBD C and C#.
What about Bb ?? 
I believe that the size of the hole has significant bearing on this (?). If the hole is too big, it won’t happen. Perhaps, try taping down the hole and see what happens. Too, I have a chanter that needed a rush once (for the right hand), rushing it made that Hard E happen easier. Obviously, a rush is going to affect tuning, but if yer just trying to see if it’ll happen, give it a go…after taping the hole.
Many thanks for that, Brazenkane! I´ll try it out and tell yous.
What about Bb ?? >
Yep, and A. And B. But the design for D C C# is different and has a stronger hard E. Mind you, the one on the A chanter is very solid.
Hunter B: very solid hard E, too.
Q&K C, nae probs.
The pleasures of chanter-fumbling: Rushed this Matt Kiernan C (fairly “heavy” rush - straw size brass tube from above F#-hole to bottom (otherwise no effect) -: Lovely hard E now but flat F# now instead 
That is my experience as well.
No E