adding missing mob models?

from what I can see in Mcreate when making a new custom mob there are a few models missing that I would like to use.

The skeleton is what I want the most.

but the ender man is also missing from the list

I also would like the old vex & maybe the shulker.

are there any pre made models you can just plug in for vanilla mob models missing from the normal list?

I know u can make a custom mob but that seems like alot to learn when I just want to make skeleton that seems like something that should be

in the list.   or is there a way to pull the model file from the Jar file of the ver I am modding for?