In the last years of the old Colony of Natal it had a system of military "Reserves" in support of its Volunteer Regiments (militia). The "reserves" came to the fore during the Natal Rebellion in 1906. For example:
Dundee Borough Reserves
Dundee District Reserves
1st Greytown Reserves
2nd Greytown Reserves
Durban Militia Reserves
and many more.
I suspect that they were simply TG's and DMT's by another name. Most probably saw no action at all, although Tpr H S Steel of the Umvoti Division Reserves was one of the only 15 Colonials 'Killed in Action'.
I wonder if the apparent increased interest in TG QSA's extends to other South African units? It would be surprising if medals with multiple clasps to local regiments that had particularly active wars were to fetch similar or even lower prices.