Is the detector handling open product or sealed packages? (I'm guessing sealed product bins or trays or bags or something). You can get away with staging some clean and sanitized trash cans where the reject mechanism is pushing out the trays. Auditors do like seeing locked bins to prevent employees from taking rejected material and placing it on finished pallets, but you can get around this with training and even labeling of the bins. Hell, depending on the size of your product and the quantity of rejects you anticipate, a couple of wire bins could be hung on the sides of the machine by one of your more creative maintenance guys.
If you'd prefer the locking type bins and can't get any from the supplier or the manufacturer, you could reach out to local metal fabrication shops to build you a set of custom ones attached to the machine itself.