A lot depends on the type of bandsaw you have, industrial machines tend to have just a couple of variations of t-slots So it might be possible to get a length of bar from an engineers supplier. However, with hobby tools there seems to be no standards, so getting in touch with the machine maker might get a result, alternatively try to get a couple of strips of material to fit the major and minor slots and rivet them together. If you know anyone with a miller - vertical or horizontal they might be able to mill a few strips for you. You could try the D&T dept. of your local high school if they still have that kind of machinery about but I believe many have scrapped that type of equipment in favour of laser cutters and 3D printers.

Richard