Eric
I know nothing of Lee springs codes but here is the relevant part of the write up in the series. However, I went to our local DIY store and purchased some suitable stock springs and cut them to length. The rear's could be a bit stifer but it runs fine.
Springs for 31⁄2in. gauge locomotives are commercially available, but will probably be rather too stiff for such a light locomotive, so the springs for Northumbrian are best made from scratch. Some 22 gauge piano wire will be about right for the driving axle springs. The trailing ones can be thinner. Winding the springs is not difficult, although it takes a bit of practice. Find a bit of steel rod about 6in. long, and slightly smaller than the required internal diameter of the spring, in this case about 3⁄32 inch. Put the rod in the 3-jaw chuck, trap one end of the piano wire under a jaw, then rotate the chuck with your left hand, guiding the wire onto the rod with your right, keeping each coil of wire in contact with the last. When you have wound about 4in. release the tension on the wire and the coils will spring evenly apart.
Cut up the coil with snips or side cutters to make the individual springs. The driving springs will need to be about 11⁄4in. free length, and the trailing springs about 5⁄8in. but some adjustment will probably be necessary when the locomotive is complete. Flatten the ends of each spring by holding lightly against the side of a grinding wheel. Now fit the axles to the chassis, and put on the horn stays.
Compress the trailing springs with tweezers, and slip them into their seating in the axleboxes. If the ends of the springs are flat, they will stay
Pete