That's the p/n 61247 cover that's common to most parallel valve lycomings from o-235 to o-540.
You can get them in black, chrome or stainless new at about $25-30 each.
If you're having trouble getting some, let me know and I'll source some in the US and get them hand carried back to the UK after Oshkosh. Gasket is p/n 75906.