Hi Nigel
I've got two that I got when I started Black Powder.
The Modern Muzzle Loader by Andrew Courtney ISBN 0-9530541-0-1
and
Black Powder Guide by George c Nonte Jr ISBN 0-88317-069-8
Have a look on the LRML site too :
http://www.lrml.org/resources/index.htm
I think the first one may be available through the MLAGB try their contacts
http://mlagb.com/officers.htm
Cheers
Roy