First, welcome to the MLS gang.
For my freelance flats, I have shiplapped decking using 1.20 3x8 stock available from Ozark Miniatures. I did it in the milling machine, with some loss due to spliting or flexing. Having seen your fine miniature woodworking, I would like to know the technique you plan to use. Would you really consider making tongue&groove in 1.29, if that's what the prototype was? Expect that you just might!