"They need other artists."
Translation:One potrzebują innych artystów.
Is there any rule to know which nouns end in -ów in the genitive plural, and which ones end in -ek? And are they other possible endings? For example : matka -> matek artysta -> artystów
there are rules, depending on the gender and the last letters of the noun., but there are also exceptions.
but the more general tables do not show -a ending masculine nouns, so you can either find some rules here http://grzegorj.w.interiowo.pl/gram/gram00.html or just learn the declension.