Goodman Games

I don't have some of the monsters listed in Castle Whiterock, they refer to some books (Underdark book, etc). Just curious if someone has good stubstitutions or better visual descriptions.

thanks

Check out appendix J (page 597 of the black book). It includes visual descriptions of every non-MM monster in Castle Whiterock.

What other sources were used for monsters?

CW drew from quite an array of products. Check out the OGL legal text on the last page of the fourth book (I believe that's where it is); if you scan through the fine print in the last column you'll see quite a few entries for products drawn from.