Simon,
I have a bag fuel tank out of a K Series S3, currently on eBay.
https://www.ebay.co.uk/itm/126337830340?itmmeta=01HQ6QDFDD3C1SCJ1BHHH8RBJP&hash=item1d6a524dc4:g:6KUAAOSw1rNlto3C&itmprp=enc%3AAQAIAAAAwO0oO0%2Fj0WjhtRPQmfNPMWWDjxP9UxzODpSRCOLxsvPwmB3CfYVmS84eQSuE7KFDpM2DlzNk1rIwpCw%2BCb2wGooF0yyBrbF1TeFEzw7XvRIl4ZtkLfWDuacUYbR702%2FZZk9zaupDoe39Z%2BQuzzeGHV1IHU4DBSZL8fTWGB%2FmY2%2BpuvwtM1l28a0%2FEQuQ75DMLk%2FqlRP9PdpRuJS43TYqhHJYUFYYX468zhMhr7qh7pgyNBkyWrBAGiBjfuICq0JPgQ%3D%3D|tkp%3ABk9SR-L2tde5Yw
Julian