I did pickup an asset on the asset store that I use for Skeletons, but for all other Undead I use Daz.
I use that for my skeleton needs.
I have some muscle maps and bones for some of the Daz characters, but it was overkill. There was also a vendor Predatron on Daz that has a decent skeleton pack, but he also requires and Indie Game Developers License and it didn't make a lot of sense to me to use his Skeletons and then pay that license fee. So I use these Mister Necturus ones which are perfect for my needs. I also bought them when Mister Necturus was having a crazy sale.