from Crys at Needlebar regarding my G&B Lockstitch
"I don't know what needle this model uses but G&B used 3 kinds of non-curved needles. So one of them should work in your machine. There is a flat shank needle known as the G&B 19. It is just about impossible to find and I don't know of any equivalents. It is 1 7/8 inches long and the flat part of the shank is very small. i.e. it's shankless. It's not much bigger than the shaft of the needle.
G&B also used 2 kinds of round shank needles. One is the 13x1 and the other is the 2x1. For the 2x1 you should be able to use LAx361."
I have put in a Boye #2 and it works great.
also, based on this serial number DB
(the webmaster says it was pulled from the digital copy of grace coopers book on the Smithsonian site)
mine which is serial number 340205 dates to 1871.