I didn't think there was anything commercially available to fit the bay1 mount - other than specific bay1 items. I'll google both and see what i find. I'd likely never use the Cokin (or Lee for that matter) over my 35mm lenses so it would be strictly for the 6x6.
Interestingly, i'd consider a Cokin/Lee for my 6x6, but never for my 35mm due to IQ degradation from the lower-quality-than-the-lenses filters whereas the 6x6 IQ *should* be magnitudes greater than my 35mm line-up. Desperation maybe?!?