Rustoleum make some great paints.
https://www.promain.co.uk/metal-pain...ant-paint.html
I used some of their Synthetic oil based Green Rattle can on a Honda CX Colour change I did,
It's more robust than normal Rattle can paint but still needs care if used on a fuel tank as although it won't melt if fuel gets on it it does mark but the marks can be compounded out so the paint is,"Serviceable".Of course fuel tanks should have Twin-Pack activated paint or clear-coat applied but it's a decent half-way house cheap solution.