Might be worth a call to BACO to see if they will run you a box. They don't always stock some stuff but will make some on order.
If they don't give you much hope for that, then Paul's suggestion of running a 45-90 case into a 40-65 die and fire forming then trim back to 2.4 is the next best bet. Might want to land and groove diameter, as those old 40's often used a .406 diameter bullet, and that might be where you run into problems loading coming up with a 260 gr .403 or.406 dia bullet.
Bullshop might be a source for bullets etc.
