I think the small book Gav is talking about is 'Sinhala Weapons and Armour' by P.E.P.Deraniyagala, originally published in 1942 but recently re-printed by Ken Trotman Publishing
http://www.kentrotman.com/indexmn.htm
It's a must have for anyone studying Indian or Sinhalese Arms.
Regards,
Runjeet