Becker Alto Whistles are available in these keys:   G, A, and Bb.   They have a delrin fipple block (mouthpiece).
I have improved the tuning of the top 3 fingerholes.  A handmade alto whistle for $18.75!

These bigger brothers in the whistle world are built to play in tune, having a solid low note, yet easily 
jumping to the higher octave.  The lower mellow sound is so pleasing on the ear!
Alto G Whistle
Plays in G and C easily.  PVC with delrin fipple block
$
18.75    
Alto A Whistle
Plays in A and D easily.   PVC with delrin fipple block
$
18.75    
Alto Bb Whistle
Plays in Bb and Eb easily.  PVC with delrin fipple block
$
18.75