I also have the camless buttonholer which is a lot heavier than the 160506; this I keep for use with the older cast iron black Singers. I have seen additional cams for sale on ebay (even the eylet cam at a very very high price) but even these are out of my price range, consdering postage...
What you're saying about buttonholers and monogrammers made for zigzag machines piqued my interest... All the one I have seen were made for slant shank machines and I would be interested to know if the same were made for low shank machines like my Starlet...