> Does anyone know of a source for an M4.5 x 0.90 tap and die?

Hi, Are you sure this is metric at all?  M4.5 is not a metric
standard in any of my books, but of course it all depends on
who made this.  Some ideas:

* 0.9 mm results in 28.22 TPI and you could use 28 TPI (0.85 mm)
without much error.

* 4.5 mm converts to 0.177", 3/16" seems to be fairly close to
that (~4.7 mm)

It appears there is a 3/16" x 28 TPI tap.  Maybe you can use that?

Regards,
Bernt Damm
Sydney