Keiviite-Yb also available – send a message if you’re interested
According to Wikipedia, “Ytterbium is found with other rare-earth elements in several rare minerals. It is most often recovered commercially from monazite sand (0.03% ytterbium). The element is also found in euxenite and xenotime.”
According to Mindat there are 6 known minerals containing large amounts of Ytterbium: