What the R312B-C actually is
The Mitsubishi R312B-C is a 12-slot PLC expansion module sitting in the PLCs and Accessories / PLC Expansion Modules class, built to take additional I/O or special-function modules into a Mitsubishi rack-style PLC system.
Production status
Production stage is current with no last-time-buy timer attached; the unit is specified into the BOM and quoted to order against an RFQ.
Sourcing posture
Order code R312B-C, current production stage, 12-slot chassis for a Mitsubishi rack PLC - the BOM line reads cleanly against the listing and is the kind of line that is handled quoted-to-order rather than off-the-shelf from a parts bin. Send the part number and quantity on an RFQ and the desk will come back with current availability and lead time against that spec.