Theyre not as rare as the name suggests its quite easy to get them

1 beaver dams (they spawn there and if you wish to farm it along with cementing paste make sure to drop things you dont want and empty it)

2 Get a theri (best amounts of loot) take it to nearby swamp look for bushes (small one which have red bulb coming out) or a bush which looks like a fern you can get a lot with theri or you can use sickle which...is not great but is wayyy better than hands (make sure to use right click att and not left or head bump)