is it possible to do a 3 way switch if power source is in the second switch?
Yes, it is possible. But you may need to replace the existing switch. The key to making it work is that you need a connection behind the existing switch between two wires.

You need to do this:


The existing switch needs to be a change-over switch, switching active.
The two poles of the existing switch are cabled to the new switch, as well as a single return wire. (That's three wires between the switch plates.)
The new switch is also a change-over switch, switching the return wire between the other two.
Behind the existing switch, you connect the return wire to the light socket's active wire. This is the connection which doesn't connect to the existing switch.


Normally you would use the loop terminal for the last point, but that might already be in use for the neutral connection. In that case, you will need an in-line connector.

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