In languages that express grammatical number in nouns with suffixes, usually there is either a suffix added to an unsuffixed singular to form the plural (cat—cats), or the suffix (or inflectional ending) is replaced (Italian gatto—gatti).
Are there, however, any languages that consistently use unsuffixed plurals for nouns and add a suffix to form the singular?
I'm aware of Arabic examples such as ghurfah "room" — ghuraf "rooms", but they're rather sporadic and involve internal flexion. Collective nouns such as al-ˁarab being the basis for ˁarabîyyun "an Arab" come closer, but I'm not at all sure they're technically the same noun in different numbers, as opposed to separate nouns.
Theoretically, I can think of two scenarios in which suffixed singulars and unsuffixed plurals could occur: one where the plural inflectional ending is lost historically but the singular one remains, making it seem as though something is added to form the singular; and another one where all of the old inflexion is lost and there is no number distinction for a while, until a partitive suffix of some sort is grammaticalised as the new singular.