Check with Rovers North. I spoke with them about this a few months back. It's available, but not cheap. It might be STC3178 ($188) but the descriptions on their site sometimes suck. IIRC, there is a "correct" buckle and there is also a similar one for the 110 that may or may not work, but costs like 1/3 the price.
Call RN - they're usually very helpful over the phone.