I just received this e-mail the other day. The only 50 speed film left in color neg. is ECN-2 process EXR-50D from Eastman Kodak. It's only available in still cassettes from RGB color lab and I doubt you can find it in any bigger size save buying thousands of feet of 65mm from EK.

Dear Customer

Thank you for your inquiry.

We would like to inform you that the Konica Minolta - KOI5036 REG - Impresa-50 135-36 Professional Color Print Film (ISO-50)
you previously registered for notification has been discontinued and will no longer be
available from B&H.

We look forward to your next visit to our site. Please feel free to let
us know if there's any other way we may assist you.

Thank you,
The B&H Web Team
420 Ninth Avenue
New York, NY 10001, USA

Sorry to have to be the harbinger of news like this.

Regards to all.
~Karl Borowski