Forgive my being disagreeable but are you quite sure? The connector at the given URL is listed as being an RJ-11 (more correctly called a 64PC) but that is not what is depicted in the drawing. The drawing shows the correct connector for the Amiga 1000 keyboard which is a
4P4C also know (incorrectly) as RJ9. It is RJ-11's little brother. It's the same cable that goes between older phones and their handsets and can be found in most electronic surplus shops.
Hope that helps.
