Hi, Gary, if you're not averse to buying a box of figures, try HaT or Italeri, both of whom have had 1/72 cavalry sets in their catalogs, including sets of Prussian Seven Years War dragoons, and Prussian Napoleonic Wars cuirassiers. Either type of figure could be converted relatively easily into a rider from our Revolutionary Wars.
Locally, I'd try Triple A Hobbies, and any Hobbytown. Our Hobbytown store up here in the Lehigh Valley has figure sets like these, so you might be able to find them off the shelf. Beyond that, you could look for vendors who sell them over the Internet. Some possibilites are Hobby Bunker in Malden, Massachussetts (www.hobbybunker.com). I know the owner, Matt Murphy, and if he doesn't carry something like this in stock, I'm sure he'll be able to find it in his catalogs.
IMain Line Hobbies, now at the Plymouth Meeting Mall, is also a possibility, though I think he stocks heavily for car modelers.
And of course, there's always eBay. The manufacturers and sets that I mentioned are usually to be found in eBay auctions, at any given time.
Another possibility, depending on your daughter's deadline, is to visit the upcoming Cold Wars wargaming show in Lancaster. The show is put on by the Historical Miniatures Gaming Society (http://www.hmgs.org/), they host Cold Wars in the winter, Historicon in the summer, and Fall-In in autumn. There are vendors at the show, who specialize in smaller scales favored by wargamers.
Hope that helps!
Brad