There was a gf.zip file of such a package posted to the list on Nov 11th
by Alasdair McAndrew.
I can email you a copy privately if you didn't get it.
Fabrizio Caruso wrote:
> Hi again,
>
> Is there a package or some specialized
> routines in Maxima for finite fields
> of general cardinality (p^n)?
>
> Fabrizio
>
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>