Cara, im pretty sure the RSM did release a collection of essays, have a look here
http://www.cafepress.co.uk/rsmshop
Also have a look at
Revolution in Ireland: Popular Militancy, 1917-1923 by Conor Kostick. Great book about Working Class struggle in Ireland at that time.
'Memories of 1981' is a small book written by Republican Socialists about the hunger stikes. Its not really about the RSM but its nice to read a book where the RSM's contribution isnt airbrushed out or ignored.
There is no branch of the IRSP in London at the moment, but they are going through a period of reorginisation and expansion, so get in touch with them via their website and im sure they will get back to you. Im in London myself and was in touch with them recently. Im sure there is great potential for the RSM in London and in England generally.