Try searching for "GWR Semephore signal" on the download station. The type you are after appears to be a lower quadrunt type (signal is cleared downwards). Also, try looking in the West Somerset Railway/Train driver package if you have it, as that does have an interesting array of signals.
For realism reasons, I'd suggest you read the instructions on how to place and use semephore signals.
Ususally, a section has 4 home signals and a Distance signals, so, in this direction
Block start|----- Distant Signal ------- Outer Home ----- Inner Home ----- Starter ---- Advanced Starter.
Usually, a signal box is placed in between the inner home and starter signal.
