Some nouns can have more than one plural form but here are a few examples of what they look like:
plurals ending in an
beachdan
brògan
dealbhan
plurals ending in ichean
gealaichean
and also notice this one> bràithrean
other endings you will see are tan, tean, annan, achan, aidhean as well as special irregular ones
Kilbirnie & Beyond 