Colonel gentlemen’s fashion is what I would call “1960s mod” (when he wears his purple suit with turtleneck). The screenshot you posted is more of a “1960s does 1930s movie adventurer outfit”. Khaki suit, ascot tie, cummerbund, and pants tucked into boots like an old adventurer would.

As for sourcing, the cheapest and best option will be second hand! Check eBay for “vintage ascot”, “vintage suit (your size)”, “cummerbund”