Take the lock to your local hardware and try screws until you find one that fits - I'm assuming that when you are referring to "lock screws" you are talking about the screws that holds the lock in to the mortise that go through the stock and in to the back side of the lock plate?
For the length - insert your lock in to your mortise and measure from the outer surface of the lock plate to the surface of the stock on the opposite side - this should be the length you need. The upper screw (that goes in to the center of the plate probably falls within the falling arc of the hammer. When you do your final assembly, just make sure that the end of the screw ends at the outer surface of the lock plate - if it extends through and above the outer surface of the plate, it may interfere with the hammer as it falls.
You don't need "original CVA" parts for this - just find a skew that has the right screw pitch and length - normally those screws are only threaded on the end - but = if you find one that is the right diameter, pitch and length that works, and it's threaded the entire length - it will still work as the only thing you'll see is the head on one side and the end on the other. I could be wrong but I'm betting that they are quite possibly a metric thread.
If a pair of '51 Navies were good enough for Billy Hickok, then a single Navy on my right hip is good enough for me . . . besides . . . I'm probably only half as good as he was anyways. Hiram's Rangers Badge #63