Peter,
I bought 2 new struts from SGS Engineering in the UK. From the force range versus rod diameter you have quoted it looks to me like you may have already looked on their website. The struts are the 10mm rod spec with 22mm housing, they look pretty similar to the original parts that I sent to SGS to measure. I had them gassed up to 350N to suit an early car with no wing, they work OK but a little bit more force would probably be an improvement. They charged me £52 with VAT and postage.
Hope this helps,
Robert
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