While you will find 1861 Navies converted to .38 from .36 precussion and originally so manufactured , he's out of look as far as .45 goes, especially if he wants an original. He might want to look at the various conversions from Cimarron, such as the Open Tops and Richards; if he'll take an 1851, they offer two version in .38 Spl. Here's two links:
Open Top Revolvers
Hope this helps.