I recently needed a replacement gasket for my OS 33GT petrol engine and could not find one in the UK so bought one from Hong Kong which with the postage came to around £7:50. However with further searching I found ICBIMProducts http://icbimproducts.com/ who supplied and delivered two gaskets for the same amount.
They are the correct profile and appear to be made from the same material.
The company have an extensive range of gaskets available for a huge range of engines.
The RRP from Ripmax is £3.75 each plus postage, but they don’t have any stock