Below some few references to web pages of especially paint manufacturers with their own paint comparison tables

Revell

This firm has a rather limited table with RAL, Polly Scale and ModelMaster / Testor and Acryllics and unfortunately not with Federal Standard or British Standard: Revell Germany Paint guide Cross Reference to Testors Paint Numbers

Note that Revell's paint range may vary over the years.

Italeri

Italeri also has its own paint range and a more extensive comparison table than Revell. Comparison is made with Federal Standard, Tamiya, Humbrol, Gunze en Revell: Italeri Acrylicpaint Color Conversion Chart

Humbrol

Deze fabrikant heeft het wat anders aangepakt.

This manufacturer has a somewhat different approach.

You can search for a colour system or paint manufacturer here, specify the colour or paint number and then you can request the corresponding Humbrol paint:  Convert to Humbrol

It is possible to downal a so-called  "Wall-Chart", in fact a PDF wiht Humbrol's paint range. There are also a number of cross tables for paint systems and other paint manufacturers