I personally never made any assets here.. But have heard long ago "if my memory working.." It wasn't too hard to make own? Maybe try to google how to edit assets and work with ones you found? This is off many year old memory since I played. But I believe when I was looking for some thing that was answer I got.

Another option is see if some one would make them for you. Used to be ton of modelers around before. Maybe find one that is bored :-)