So I’ve been itching to make some whistles lately and I’d like to get my hands on some inexpensive/dirt-cheap fipples for practicing. I searched the posts but didn’t see this subject. Anybody know where I can purchase wholesale/supercheap fipples?
Depends what bore size. Sometimes you can find dowel exactly the right size, but usually it’s a D.I.Y. job or perhaps a friend with a lathe could help. You can always cast your own using polyester resin.
Are you talking about whistles in the “low tech whistle” style, made from PVC tubes? I have started making fipple-less version of them by putting the labium edge on the outer surface of the tube, and fixing a strip of PVC tube on the outside of the whistle tube to form the windway. In this way I get a better range and better tone, and I don’t need to hunt for dowels of the right dimension.
I play one of these in http://www.youtube.com/watch?v=C1f-8ZTl8Tw Mind, the tuning is a traditional Scandinavian “blue” tuning, so it might sound out of tune to your ears.
I put out some “how to”-pictures showing the fipple-less whistle at http://www.youtube.com/watch?v=-JN_vMXSP10
Yes, interesting. Of course, it’s still a fipple, with a circular window and the tube body acting as the block. 
I imagine that by thinning the tube from the window to the head end, you could lower the windway with respect to the blade, and gain a bit more control over voicing.
I’m curious whether the OP is asking for fipple material or the entire plastic mouthpiece.
I think the OP is asking where to buy, say, a bag of Generation whistle heads (not fipples) so that s/he can practice making tubes for them and/or tweaking the voicing.
The Whistle Shop sells several types of tops listed as whistle mouthpieces.
Yes, interesting. Of course, it’s still a fipple, with a circular window and the tube body acting as the block.
Yes, I suppose that the term should be “fipple-block-less whistle”. A bit cumbersome, perhaps. How about an “exo-fipple whistle”? 
I imagine that by thinning the tube from the window to the head end, you could lower the windway with respect to the blade, and gain a bit more control over voicing.
Good idea, I’ll try that. And I do hope that someone will give this thing a try and share their experiences.