Highland is also struggling on its pound;135,000 allocation to meet the Executive's election commitment to give primary pupils a chance to play an instrument and is to devolve the initiative to Feisean nan Gaidheal, the Gaelic cultural organisation that runs workshops in schools.
Two weeks ago, Moray reported similar difficulties and questioned whether to proceed when there appeared to be no extra music instructors prepared to work on the council's patch.
Nationally, it is estimated there is a shortage of more than 150 instructors if the pound;17.5 million scheme is to be implemented as ministers envisage over the next three years.
Murdo Macleod, Western Isles education director, said: "The Executive's aspiration is noble and high but the funds do not really match it." The authority has been given pound;24,000 but this is set against its existing limited instructor service budget of pound;200,000.
There are currently only three Gaelic singing staff, three piping instructors and one brass instructor to cover primaries.
"It is unrealistic to raise expectations that a full and comprehensive service based on the existing model can be achieved," Mr Macleod told councillors at this week's education committee.
The council is to look for sessional instructors who might be prepared to offer lessons at lunchtimes or outside school hours.