https://annarchive.com/files/Drmg120.pdf
Page 42
This was cited previously by, Hey I Can Chan
Has an entire list on the subject at hand, the materials, and tuning of the tuning fork, or "forked rod," which is exactly a tuning fork anyways, this is old lore, and may not be relevant in 5e.
One of the editors is Ed Greenwood, the setting you're playing in 5e is forgotten realms for the most part, his setting. This passed by his editorial desk and was approved for dm120 1987. Also, Jeff Grubb has done work with Ed Greendwood before in the Forgotten Realms setting. He was in charge of the original Manual of the Planes, and also had a lot to do with Spelljammer. Back when it was TSR, and not Wizards of the Coast.
https://en.wikipedia.org/wiki/Jeff_Grubb
Was on my phone before, so apologies for the lack of links to cite what I said, re-reading it, it looks a bit like a mess.