Reproduction mortar available here (although I don't know how good):-
http://www.milweb.net/dealers/trader/anti_tank_gun_replicas/
A few items on this link may interest you:-
http://www.bocn.co.uk/vbforum/archive/index.php/f-13.html
Copied from link below
This publication consists of two pamphlets on the British 4.2-in Mortar - the basic training manual (1943) which includes the training and use of the mortar, and the detailed handbook (1944) on the weapon, which includes details of the mortar, sighting equipment and, most importantly, the mortar bombs. Well illustrated and full of the detail needed to understand how it was used and what it could do.
http://www.mlrsbooks.co.uk/bookstore/product/item675.html