Is glasses only a plural noun? We can't say a glasses right?
What about a matches and a tissues?
If you're referring to a glass you drink out of, there are both singular and plural forms:
He drank a glass of milk.
She brought out several glasses for iced tea.
If you're referring to what people wear to correct their eyesight, then there's only the plural form.
My glasses don't fit right.
He'll get his new glasses on Tuesday.
Match/matches -- both singular and plural forms, yes -- but you don't use "a" with the plural form.
He struck a match to light the campfire.
They brought matches, but they all got wet and were useless.
Tissue/tissues -- but you don't use "a" with the plural form.
Please, hand me a tissue.
Would you pick up a box of tissues at the store for me?