Actually, a good proportion of the gouache sold is not ASTM I or II. (lightfast)
The recent history of gouache has been that it has commonly been used by designers and graphic artists who do not need permanence in their work, since it will be used for reproduction, and not hung as a finished work. This was not always so, and of course many great works have been made using gouache or so-called body colour.
Some manufacturers put the pigment used on the tube. Even fewer tell you which of their gouache paints are lightfast in their literature.
The most commonly questionable pigments used in gouache tend to be amongst the cool reds and violets. M Graham publish details of their artists' gouache here:
(Just look for the 'G' in the listing for the paints that they supply as gouache).
Art Spectrum publish their gouache pigment information here:
It is generally thought that BWS scale results of 6 or above are more-or-less equivalent to ASTM II or better.
Both Art Spectrum and M Graham appear mostly to rely on pigment concentration to achieve opacity, rather than using a lot of fillers or opaque additions like chalk.
There may be other manufacturers who do the same.
Since gouache is very similar to watercolour, you can for example substitute a reliable cool red from an artists' watercolour range, and so on. The essential difference will usually be in transparency, but colours can of course be made more opaque by adding white, powdered chalk or a similar opaque pigment.