I believe Martin only began building guitars braced specifically for steel strings in 1922 so anything prior to that date will be braced less heavily and consequently will be more responsive to the lighter tension of nylon strings.
Good luck with your search but I think, as has been suggested, you'll have a much better chance of finding something in the USA.
Early Martins, if they do ever show up here, are either grossly overpriced or snapped up very quickly by collectors-frequently before they even have a chance to get on a shop wall.