This quest is going to be tricky, from several perspectives. Every neighborhood needs a town clown, and in my mishmash BBC-show hood, that clown is the "amateur dictator" Roderick Spode. His vision of a new British global dominance is mostly based on root vegetables and umbrellas. What a maroon.
ANyhow, now that I've established that I do not espouse his dimwitted fascist ideals, I would like to try to simulate his costume. Slightly different than my earlier need for a short-sleeved khaki safari shirt for Higgins, the uniform of the "Black Shorts" includes a khaki long-sleeved army-type top, and of course black shorts as a bottom. Because the Saviours of Britain (Spode's legions) are British, they also wear knee-high socks and sturdy boots with their shorts.

I've now uploaded the photo, for what it's worth. It's not a particularly good one though: a pixelly screenshot from Jeeves & Wooster. Just remember that the khaki shirt should be long-sleeved, with a collar and possibly a tie. The shorts should be black, preferably with socks. The only way to accomplish this would be with separates... unless some weirdo has already produced a Sim Spode, that is.

Below, Spode harangues an appropriately skeptical crowd in Hyde Park, no doubt on the subject of shapely knees and ovine rail transport. The listeners reach for their rotten turnips...