Welcome Englishbiker!
I buy most of my parts on Ebay, Amazon or AliExpress. For example, you can find a rubber cam belt like you describe here:
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https://www.ebay.com/itm/GATES-TIMIN...IAAOSwFdtXxad8
And you can get the gears as well:
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https://www.ebay.com/itm/HNBR-Racing....c100005.m1851
Stein :-)