There was a diary for the NP Field Force during the Boer War, but it was lost.
I can send you write-ups about other men who served in the NP during Buller's Natal Campaign. They should give you an idea about the types of men who served in the NP at that time, and about some of their activities. If you do want to see them, please PM your e-mail address to me.
The NP, and its forerunner, the Natal Mounted Police, have a short but remarkable history. The 40 years of their existence (1874 to 1914) were the last great ones for the British Empire and its loyal Colony of Natal. During that time the NMP/NP fought in three wars (AngloZulu and both Boer Wars), and two rebellions (Basutoland and Natal). Apart from providing an escort for General Buller, the Police also escorted the delegation that annexed the Transvaal in 1877, and the Empress Eugenie when she visited the Prince Imperial's grave in 1881. There is lot to be proud about by being related to a man who served with them.
Regards
Brett