Many thanks again for the sage advice, I couldn't have got it more wrong if I really tried lol!!
I have managed to locate some OEM Honda Reed Petals thanks, they state they are for the MC28 only, but given the MC21 Reed Valve shares the same Part No. to the MC28 I will get these.
Just as an aside though, I did manage to find some TYGA Fibre Glass Petals, but haven't managed to locate any Carbon Fibre Petals. Are these available or do you have to adapt other Reed Valves fitted with Carbon Reeds (just a thought)?
Many thanks
Philip