@reccetrooper
In 1961 South Africa became a Republic and left the Commonwealth of Nations. In 1963/4 the United Nations imposed an initially voluntary arms embargo on them due to apartheid. The sanctions became mandatory in due course. Prior to the sanctions a lot of ordnance stores had been sourced from the UK. With the imposition of sanctions, South Africa was forced to start manufacturing their own stores, acquire them by covert means or obtain them from the black market.
A 1964 list of South African monograms makes no mention of "LP"
It would appear that up to 1961 South Africa was reliant on the UK for the supply of CS stores.
It is possible that "LP" is merely a 'cover' monogram to protect suppliers acting in contravention of the sanctions.
However, South Africa did have a firework manufacturer namely - Ronden Manufacturing Company which was established in 1948, they went on to manufacture military pyrotechnics and in due course were purchased by Armscor and renamed Swartklip Products. Subsequently became part of Denel.
"Denel Swartklip has been engaged in the research, design, development,manufacture and proofing of pyrotechnics and explosive devices for nearly half a century. Its products include a comprehensive selection of riot control, high explosive and phosphorus devices, as well as pyrotechnics for signalling, screening, illumination, training simulation and battlefield application. Swartklip is the supplier of low velocity and high velocity 40mm grenades to several countries around the world, including Europe."
Assuming I've got the right Swartklip, it is located in Limpopo Province - LP
TimG