Can I assume these are 8 ohm speakers?
I would assume its 8 ohms, if you have a volt meter the dc resistance should be around 5 or 6 ohms for an 8 ohm impedance.
Most likely the exact replacement to match the other one will be a difficult find.
Companies like Tang band have a slew of driver choices and may have discontinued the one in your speakers.
Tang band makes several drivers that would work, but you would have to buy a pair, they are pretty cheap, maybe $30.
Ebay may have cheaper ones.
Measure the cone diameter if its a 3" a Tang Band W3-593SF 3" Full Range would work.