Hi Kevin,
I appreciate how frustrating it is to not get any responses to questions on the forum, so I thought I'd at least answer and give you the benefit of my minimal experience.
Firstly, I would really recommend using the search function. This question has been asked before numerous times, and this perhaps is why the people with all the experience get fed up of repeating the same answers.
That said, the long and the short of it is Miller electrics are very hard to track down. There are alternatives to the Miller points, but they may require modification. Eddie suggested some alternatives in a previous thread, and based on that I found
http://store.heinkel-trojan-club.co.uk/opencart/index.php?route=product/product&path=20_66&product_id=590 that may or may not work - I haven't had reason to purchase any yet to find out. From memory, some late Velocettes also had Miller ignition, so the Velocette club may also be a source of assistance.
As for upgrading, the easiest upgrade to the ignition is the Honda coil upgrade which has the benefit of not using the distributor cap or rotor for distributing spark, although they remain in situ. The points are still used.
The next step up is to try and find a Lucas distributor that could be modified to fit, and may then have electronic points available.
The ultimate is to turn up a new distributor body on a lathe that can take electronic points. I know one forum member has done this.
I hope this helps, but as I say all of this information comes from repeated searches on the forum.
Andy