I just checked my older Zuiko 75mm lens against the lens diameter on my Mamiya Automat 6 (Mamiya Sekor lens). They are the same diameter (35mm) with a straight barrel. At one time I had a set of three press on filters in a blue plastic Mamiya case and a mamiya press on hood. These come up on eBay once in a while.
It seems to me, however, that the last models of the Mamiya Sekor lens on the Automat II had a tapered barrel on the front element, right up to the front, making press on filters/hoods not possible.
The Automat in the link you posted is the early Automat 6 which still had the Zuiko lens. If you are looking at a Zuiko lens Mamiya 6 or an early Automat with the Mamiya Sekor flat around the front element... look for 35mm press on attachments.