Try www.modelsignals.com - this is Model Signal Engineering who make a wide range of signal components in various scales. You do need to be able to handle a soldering iron to build them.
The book 'Constructing and operating Semaphore Signals' by **** Nicholson, published by Booklaw Publications of Nottingham, ISBN 1-901945-31-6 in 2004 is a useful reference, as is 'Model Railway Signalling' by C J Freezer, published by Patrick Stephens Ltd (PSL) in 1991 (ISBN 1-85260-174-4). This last book is out of print but can often be found second-hand on bookstalls at exhibitions and the like.
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