I know feck all about hi capas but patrolbase have this if it's any help
https://www.patrolbase.co.uk/laylax-custom-extended-slide-stop-for-hi-capa-and-1911-gbb
and fire support have these
https://www.fire-support.co.uk/product/guarder-steel-slide-stop-for-marui-meu-and-hicapa-black
https://www.fire-support.co.uk/product/laylaxnineball-tokyo-marui-hi-capa-5143-custom-slide-stop-black