Here is a very high quality 415.3 Hz tuning fork by Walker which I have used for many years in tuning harpsichords to low pitch. It's a tad pricey ($26) but you can't find a better tuning fork. https://www.indigo.com/tuning_forks/music/flute-tuning-fork-G-Sharp-415.3Hz-33917MS.html David C. Kelzenberg Iowa City, Iowa, USA
