Valmy Prussians just don't exist at 1/72nd scale. In fact, I'm not sure you'd find them at any scale in any medium. They were an odd proto-bicorn called a kasket, basically a narrow-brimmed round hat with the front and rear turned up, presenting a semi-circular silhouette (not to be confused with the false-fronted shako the Austrians called a kasket).
i think Foundry did a nice range of French Revolutionary War figures about 20 years ago, which included Prussian musketeers and Fusiliers in Kasketts. Really characterful and nicely proportioned. I had a look on their website, but they don't seem to be available any longer.