Mithril grapple: where to get it

Source	Quantity	Chance per roll
Angry barbarian spirit []	2	3/123
Berserk barbarian spirit []	2	3/123
Chewed bones []	2	6/128
Dried zombie []	1	3/128
Enraged barbarian spirit []	2	3/123
Skeleton (Ullek) []	1	3/128
Skeleton brute []	2	3/123
Skeleton heavy []	2	3/123
Skeleton hero []	2	3/123
Skeleton thug []	2	3/123
Skeleton warlord []	2	3/123