Guardsman, and Household cavalry footwear, are rather like the lawns outside stately homes; a mere few years of TLC and attention makes them shiny and black, in the case of the army, and verdant and green in the case of stately homes.
As I suspect you have neither a country pile, nor a service background, of any sort, I would suggest a trip to any emporium that sells plastic slip ons to the public. A touch of Mr Sheen and you will be shiny as a soldier. Also better turned out than the average tramp and dog ensemble. Albeit not held in the same esteem.