You have the groove dimensions, but the catalogue stops short of the diameter you need. That does not mean the machine needs a new gland.
Start with the ring's internal diameter and its cross section. A large ring can be made to a non standard diameter using joined cord or a moulding process. One supplier route is compression step moulding, sold as the CO.SM.O range, which makes large rings without cut and joined cord. These are different products. The size, quantity, duty and tolerance decide which is sensible. A standard moulded ring should still be checked first. It may be cheaper and quicker than a custom part.
Acumen's current site says it offers made to order rings from 200 mm internal diameter with no minimum purchase. That is a supply claim, not a promise that every material and cross section is immediately available. Confirm the compound, method and delivery date against the actual enquiry.
For a replacement, send the groove dimensions rather than just the old ring's measured diameter. A ring that has been in service may be swollen, flattened or stretched. State whether it seals a static cover, a moving part, gas or liquid. A size that fits is only the first test. The ring must seal the duty.
Related: large diameter O rings, what to send for a large O ring quote and the guides library.