I know of no source of parts for classic 'hand made' shotguns and of course it will depend on the nature of the mechanism but assuming a 'Southgate' derivative, the 'V' springs can be very simple, the two challenges commonly seen are the fixing method and then regulating the springs' actuating surfaces to achieve best timing.
Fixing often used side pegs on classic English guns which means a whole new spring, complete with side peg is required and that means proper metalworking skills. The simpler locating/fixing methods make the job much easier.
Regulating a spring that fits is actually pretty simple once your got your head round what is happening: that is why Southgate ejectors became the most successful ejector mechanism, bit like the Purdey Bolt/Scott Spindle.
I'm not saying that this a job for a tyro but it certainly is within the skill set of any real gunsmith.
