Hi Neil,
This may not be Irish but it is certainly a Celtic flute tradition, currently going through a resurgence.
Look to Galicia! Requintas are these flutes in F, G (old pitch) and G that the Galicians in NW Spain play with their Gaitas. I am too, as I am very much into Galician music more than any other kind (as far as playing is concerned). These flutes are essentially based on the old Napoleonic era military band flutes from France that were left behind after the French were kicked out of Spain. In the 1920s the Gaita bands wanted to spice things up a bit by adding Rumbas, Fandangos, Tangos and even Foxtrots to the repertoire and wearing the modern dress instead of traditional village costumes. Keeping up with the times. This music eventually petered out thanks to Rock and Roll not to mention Franco’s suppression of Galician music (ironic since Franco was from Galicia! Just musically uninformed) but is now undergoing a resurgence, including on the west coast of the US, thanks to efforts by some of us out here.
Here are a few links. This first is one of the best bands reviving this tradition “A Requinta de Xian”, led by Pablo Carpinteiro. He’s a great Gaita player, maker and researcher who is also doing the same with the Requintas. This video was broadcast in Galicia a few years back and is in Gallego. But still very much worth watching.
See https://www.youtube.com/watch?feature=player_embedded&v=YrTCd03XH1o
Here is my friend Cano (Alexandre Cadarso Suarez) from Galicia talking about a G Requinta that I made for him in 2011.
See http://www.youtube.com/watch?v=fGPzHOvRR3o
This last spring he ordered an instrument in F, with 3 keys. For years I have used an old American made Firth flute in F as my template for these higher flutes. However, the Requintas play up into the 3rd octave and require slightly smaller bores. This summer I found a continental-made flute on eBay that was perfect and this became my template for several Requintas, including Cano’s new one. Reaming involved using an old Napoleonic-era Belgian bayonet as the reamer. Here is a picture of the finished 3 keyed requinta and the bayonet I used.

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I made a number of keyless versions including prototypes and brought these with me to Lark Camp. Cano taught us there as well as at a 2 day Gaita Symposium in Berkeley after Camp. We performed at the end of this at the Freight and Salvage. Here is the concert, recorded with my GoPro cameras so the audio isn’t the best. We play the Requintas around 40 minutes into the second half of the concert.
First half: http://www.youtube.com/watch?v=tB-zzc__de8
Second half: http://www.youtube.com/watch?v=O1NiBcbCyM0
Cano has also written a new book of Requinta repertoire. Here is a link to that:
http://www.gaiteirosgalegos.com/index.php?option=com_content&view=article&id=2357:presentacion-de-a-requinta-adobadaa-bertamirans&catid=27&Itemid=18
Let me know if you want more information on Requintas.
Casey