C-Spanner for Colchester Student

I would like to swap chucks and I don't have a C-spanner.

It should be around 5.5" or 140mm diameter and would be grateful for any pointers where I could get one.

When I had an LO fitting Colchester I got a C spanner flame cut at a local place, then case hardened the pointy bit.

AWEM

I'm starting to realise how scarce these beasts are!! Even adjustable C-spanners only seem to go up to 120mm diameter.

In the end I used some very large stilsons which worked rather nicely and have managed to swap the chucks over.

I though case-hardening was exactly that, being more or less a suface effect with very little penetration, and would have little effect on strength?

Many thanks for the idea. What thickness steel did you use?