why don't you not use here genitve
there is always accusative after "mamy"
genitive is after negative - "nie mamy"
Why wouldn't Mamy twojej gazetę also be correct for singular you?
'twojej' is Genitive. You need Accusative here: Mamy twoją gazetę.
Dziekuję! That's very helpful.
Where can I find a table of the declensions for 'gazeta' ? I have looked but cannot find them.
(strange, the table on English Wiktionary seems to be broken...)