Mate MBK MBW are the subject of about every third post in the rolex area, if you have to ask where to get one then you dont know enough yet to build one, and i am not trying to be sarcastic in any way, If you are going to build one you need to know about the crystal to use, crowns and tubes and movement moddes what year you are basing it on as that will affect the date wheel overlay you will want. It becomes more than just a simple project after a while as you hunt for the gen parts or the perfect hands ect.
I only got in to building MBWs after trading for some ones project that he did not want to or could not finish, with out a bit of research yours may just be one of them
to see what it could be like when you have almost finished look at the comparison in my sig