Where's best to look for historic non-familial tartans?

[Old Building Prof]

Hi there. As a sort of follow up to my newbie post about deciding which tartan(s) to use, I was curious where to find historic tartans (associated with districts etc.) still in production? For example, if I search The Scottish Register of Tartans for Hebrides, I come up with all sorts of interesting patterns that are in various historical collections. Are there any manufacturers or stores which particularly specializes in such things?

By way of explanation, since my many Scots ancestors arrived in Appalachia before the Romantic Era Celtic Revival, I'd be happier when choosing my kilt material to have one in a tartan that is documented to a very early time, but not clan or military affiliated. Thanks!