As it's a matter of cutting and doesn't need perforating you might also ask Adox, perhaps via the Fotoimpex site. They have a smaller cutting and packing operation than Ilford and you might be able to get one of their emulsions slit to 70mm - I'm not sure if they have a 400ISO speed though. What will you be using as backing paper for the 116/616? Errrm, does it even have any, I don't know?!
Edit: Coincidentally I have just noticed
this product. It is a 70mm, unperforated, slow, contrasty ortho film that could perhaps give a period look to your pictures - and it's available in-stock now, but not in the US of course.