I hope that you didn't loose the spring and plunger when you took the toolpost off the Top Slde!
Take a GOOD look all over the floor and in every corner!
One of your photos shows the grubscrew that closes off the hole on the outside of the toolpost.
If you cannot obtain spares from RDG / Myford, you will need to make a replacement, and find a suitable small spring. (Again, you could make one from some piano wire.
The Pawl will just be a short piece of round bar with one end filed at an angle to suit the ratchet wheel. For the sake of durability, Silver steel would be better than mild steel. Go to Cromwell Tools and buy a 13" length and start building up your store of metal that "Will come in handy one day".
If you had the dimension of the spring (Can anyone tell Chris? Wire gauge, OD, free length, no of coils  
a) you could get one made. (If they are still trrding, Vincent Springs of Peterborough, would oblige, I am sure )
Howard