Over the years I have obtained various whistles made in India,Pakistan and the far east.I now have acollection ranging from low Ab to high Eb and most of the chromatic keys in between. These whistles are cheap and some have a great tone, but the quality is quite variable so you nearly always have to select from many and "tweek".They'r normaly made of bamboo and you sharpen a note hole by burning(with red hot Iron rod of the appropriate diameter)on the upper edge of the hole,and flatten notes with tape.To alter the bottom note(open end)remove a small ammount at a time using a sharp craft knife till you get it in tune (do this first before altering the other notes).I've seen these wistles for as little as 50p so you can afford to experiment to perfect your tweekology.The better standard of whistles cost a few pounds from Asian shops such as "Allspice" in Bradford and some Oxfam shops.Some of these have a key indicated by a letter but they'r useually a semitone lower.I had to go through a lot before I got my collection but it was well worth it,and in the process I learned to be in charge of my intonation.