Spindles? I personally would not use SS as material for a motorcycle axel, however...

As to finding parts for a Norton, almost all the parts are still available.  My ex Bill Young 1948 ES-2 parts were all easily available a couple years ago.  Try Google for Norton Clubs.

Dr. George Cohen at  geo@norton.uk.com   can ship you anyting you need and he is affordable and reliable.  

Rod

By "spindle" do you mean hub or axle? And what was the original material?

Many thanks evelrod and swall. Spindle is the UK term - I believe it's known as an axle in the US. It's the solid rod on which the inner races of the bearings are mounted. And I don't know what the original material was as I don't have an original....

Evelrod - why not SS? And have already contacted George re some other queries (am a member of the NOC).

Best of luck on the restoration.  I know it can be very taxing and expensive, especially over here.
I did not use SS as it was too soft.  I did machine up a shaft for my Model A Ford water pump from SS a number of years back and it wore heavily in the seal area...not directly relating to a Norton axel, but enough reason for me to look for better material.  Both my axels are OEM NOS from Oz. Sorry, but I don't have the email address handy. I found them through the NOC of Australia. Oh, I also switched to a 19" in the rear and a 21" front since I could not find any 20" tires.  I use a Dunlop rear and and Avon front.  So far so good.

Rod

You could use 410 stainless, which is a martensitic grade. You can buy this material pre-hardened in the Rc 26-32 range, if I recall.This would give you something with 125,000 psi min tensile strength.You could also use 416, which is the free machining version.

I would NOT use 416 for this application.  Try 17-4 PH in either the H1100 or H1150 cond.  You can buy it in the softer sol. ann. cond. and machine it, then perform a simple low-temp. HT in an air atmos.  17-7 in the H900 would also work and be even stronger, if you need the strength.  I would NOT use 17-4 in the H900 cond.

My thoughts on the 416 were in consideration of threading the axle end, as most motorcycle axles are made this way. Given that the Norton might be using a British Standard Fine thread, it would be easier to cut good thread on a piece of 416 than 410 or one of the other stainless. And since this is a restoration,I am assuming that it will not see heavy usage. I do the m/c restoration thing my self, as a hobby.Made a front axle for my Indian Chief out of 300M, but that's another story.

17-4 would be a good choice for a spindle, although I wouldn't use H1150, because there is no hardness diffenece between Condition A 17-4 and 17-4 heattreated to H1150.
So you can't verify the heattreat with a hardness check.
 I believe Mil-spec 5 warns against 17-4 H1150 for that reason. The higher heat strength treatments also I think lower the corrosion resistance of 17-4 (and 15-5) Where I work we use tons of 17-4, and our standard heattreat is H1025.