Since Forest Ronaros ring is 0.02% drop at best. And i got about 10 of those now. I would say Ron's Tintinnabulum is about 0.0005% drop like the compass part. Might be lower.

This piece took me 34hrs and was on main rotation. i had a loot scroll running the whole time.

Finally got it! It took me 39 hours to get this. Each time with a loot scroll and Kamasylve Blessing. It dropped right after the loot scroll expired, so only loot boos I got then was Kamasylve.
Bout the smaller piece's I did 12 hours before the pity system started, then dropped 82 pieces (Tranquil Tinniolum)(in 27 hours), 68 forest ronaros rings, 3 Specter's Energy and 2 greater marni stones. I was counting the killed mobs by marni stones, and it was around 105 348, playing as a Awakening Striker, so you can imagine more or less my grind speed (the amount of killed mobs is not only for Guardian and Catchers due to AOE, but I tried to killed as less of the other mobs as I could). While Pity system was on, except of normal loot scroll I had 10 hours of red +50 drop rate scroll, 2 hours of red 100%, 8 with GM's blessing, 6 hours of Villa 50% buff, and 5 hours of Black Spirit's event 22%.
Maybe someone will find this useful