Even if the gib is missing, the empty space that it fits into can be measured/gaged to get a rough but close idea of the dimensions, then cut the metal a bit oversize in all directions (more with length,) and then get busy removing material from the rough gib after marking up the parts with ink used for scraping. Remove metal from the gib where the ink is transferred, and then repeat, Anyone making a gib fit will need to have continuous access to the void for measuring and testing as the work progresses. A gib is not really something you can call on the phone and order, unless somebody makes gibs to roughly fit your Van Norman machine (I think that is quite unlikely), and the gib would still need to be custom fit to the existing void.