Try these guys for the safety:

http://www.kwk.us/FA/

I know nothing about them other than what is on the site.
They do have Gibbs farq. listed below all of the pics.

Is it in sporter configuration or a target rifle?
If the barrel is a nice original style contour, I would be inclined to get the forend done, then the safety. I never saw much need for a safety on a target rifle anyway.
Shoot it as a 45/70 and see how you like it - would be very economical and would merely postpone your plan to return it to original configuration, which is commendable. Unless the barrel contour would be so different that you would have to get another forend done for the .461 barrel.

Oh yes, please post some pictures...