My Steinway action has pivoting flanges joining whippens to keys - piano is 1864 - are these still available or is there a more modern straight replacement?

Also, please can I have some advice about how will I know whether the strings are beyond their best - is there a particular dull sound I should listen for?

Thanks

There are no parts for an 1864. A modern action would need to be made to fit. If the strings are all original, than they're well past their prime. 25-30 years with even moderate use is considered the average life of piano wire.
Why don't you just get the piano rebuilt, at this age, it needs it, if there has'nt been any previous work done to it.