Dear Arthur,
I think, your problem have two possible solution. The more sophisticated is buy the focus screen "Beattie" which is probably the best of the world, produced by Morco, but it is a very expensive, more than 200 Pound. Link:
http://www.morco.uk.com/latest/beattie.htm Cheaper, but also perfect solution, is buy focusing screen which are producing by Mr. Rick Oleson. This focusing screen cost only 30 USD. Link:
http://rick_oleson.tripod.com/. I have focusing screen from Mr. Oleson and I am absolutely satisfied. It is fantasic. I have Mamiya C 220 and both producers offer focusing screen for this model. I am not sure if your screen for Mamiflex C 2 is identical. If it is different, perhaps it would be possible to order. I hope this information can help you.
Cheers
Krystof