Cornet in A?

Clarinets commonly use two keys for their instrument - Bb and A. However, Cornets, the lead melody section in concert bands and brass bands, only seem to use a Cornet in Bb. This would be normal - after all, there is no Trumpet in A - but I have found records of Cornets in A existing. 

Recently I was looking at the score for Elgar's Land of Hope and Glory. The opening clearly shows a brass section of 4 Horns in F, 2 Trumpets in F, 2 Cornets in A, 3 Trombones and a Tuba.

Secondly, the ABRSM Music Theory in Practice: Grade 5 book shows it. The transposition chapter includes transposition practice for Clarinet in A and Cornet in A.

So, are these instruments widely available? Is there any use for them over the standard Bb Cornet?

Maybe I'm just an idiot, but I've never heard of one in A. This website even calls it "obsolete". Don't use it, I guess.

http://utminers.utep.edu/charlesl/transpose.html

That's just what I needed to know! I guess it was just used as an example in the book, as there are few instruments pitched in A. Thanks for the link, it has some useful information.

il y a deja eu des cornets en la mais plus aucun manufacturier de trompette/cornet en produisent

I have heard from a family member about cornets in C and D (and I think B flat too) being used in Spanish procesional marches, but it might be wrong.