I've investigated this too. Most of the alternative glyphs with the word 'colon' in the description are decidedly unattractive as a colon replacement (`˸`,`܄`,`﹕`,`᠄`,`：,`︓`, and `꞉`). 

There is another alternative that at least has a similar character width to the original colon - the mathematical symbol for a ratio:  `∶`. It looks great in a number of monospaced fonts, but it is a little small in the default MacOS system font. 

Here it is being used in a file name:

`/Users/me/Books/Book Title: Book Subtitle.pdf`  [restricted colon glyph]
`/Users/me/Books/Book Title∶ Book Subtitle.pdf`  [permitted ratio glyph]