My manual collecting got somewhat (!) out of hand at one point, though the material on offer through eBay and Abebooks seems to have tapered off over the last few years. (That may be due to my depredations, of course.)
The late (and sadly missed) Alister Mitchell (GM3UDL) did a lot of the scanning for the archive, but there's still a fair amount left to do and I haven't had time to get stuck into it recently. Hopefully this will change soon.
The archive list for the Signal Training stuff is here:
http://www.royalsignals.org.uk/signals.htm
Most of the Signal Training documents on there are my collection. (I'm trying not to think how much it cost.)
I have a selection of the earlier 'vest pocket sized' Signalling Training books, but they're in poor condition and tiny type size so that scanning is difficult. It will happen eventually. (1907 - 1915, I think).
Chris.