Rambeau Tufts can be obtained from Rambeaus of course, either by killing them or taming them and harvesting from them after they have become your Pets.
Rambeaus are peaceful blue goat-like creatures living on high Mountains and spawning on Peakstone mostly during the (ingame) day.
Rambeau Tufts are needed as ingredients for crafting-recipes like Fire Resistance Potions, Diamond armor and Freeze Bombs.
This material cannot be put into your quickbar and cannot be placed into the world. It also cannot be displayed on Wall Shelves, Wood Planters or Flower Pots (as of R26 in December 2015).