Do you specifically mean a masterbuilt by Warwick, of a Thumb NT 5, or do you just mean a Thumb NT 5? The Masterbuilt is a fairly recent designation, there aren't many around for sale second hand, and they are very expensive. However, a Thumb NT 5, before they invented that grading system, there should be plenty around on the second hand market, there is basically no difference apart from some nice add-ons like wooden tuning pegs compared to the previous NT models, lots of models that are now only Masterbuilt (I believe all NTs by Warwick), existed before that designation existed, so unless you specifically want those metal plated pickup covers and wooden pegs, I would look for a second hand Thumb NT 5, they are basically the same instrument other than some older NT models may be ovangokol, not bubinga and wenge, depending on the era. By natural stain do you mean oil finish, or something else? There will be plenty of oil finish ones second hand, as it's been their standard, however satin, colours etc, are much more uncommon and will probably require a custom shop order, or hoping to find someone's custom shop order sold second hand.