Here is the text from the novel (see Malcolm Douglas' link above):

Leroux, J. Robert. Murder in the Glen: A Novel. Burnstown, ON: General Store Pub. House, 2003, page 150:

When the simmer bricht returnin'
Decks each grove and buddin' tree,
When the birds amang the branches
Are a-pipin' loud and free,
And the bairnies fu' o glee
Pu' the roses in the den,
O! 'twere dear delight to wander
In my bonnie native glen.

At the early peep o' morning
When the grass was wat wi' dew,
Among the woods o' hazel
Gaily sang the shy cuckoo;
An' the calves, clean daft wi' joy,
Gaed a-friskin' roun' the pen—
Now we've nae sic scenes o' gladness
In my bonnie native glen.

In the gloomy winter e'enin's,
Roun' the ingle gathered a',
An' wi' music, mirth, an' dancin'
There we wiled the hours awa';
Or the auld folks aiblins tauld
O' the brave an michty men
That were ance the pride and glory
O' my bonnie native glen.

Now the dwellin's are in ruins,
Where ance lived a gallant clan;
Theirs was aye the fren'ly welcome,
An' theirs aye the open han';
Aft the needy an' the puir
Found a place at their fire en'—
Now, alas! there's nane to greet them
In my bonnie native glen.

But fare ye weel each fountain,
Each dell an' grassy brae,
Where aft the kye I herded
In boyhood's happy day.
When life's gloaming settles down,
An' my race is at an en',
'Tis my wish that death should find me
In my bonnie native glen.

I also found this quote in

Cooper, Derek. Hebridean Connection: A View of the Highlands and the Islands. London: Routledge & Kegan Paul, 1977, page 3:

Although the heart may be in the hills, few expatriates in their right mind actually contemplated living there. "'Tis my wish," wrote Neil MacLeod, "that Death should find me in my bonnie native glen." But until that time he was happy enough in Edinburgh.

And this quote is given in

Gaelic Society of Glasgow, and Neil Munro. The Old Highlands; Being Papers Read Before the Gaelic Society of Glasgow, 1895-1906. Glasgow: A. Sinclair, 1908, page 327:

The paper is "The Songs of the Gael" by Henry Whyte ("Fionn.")

Of the sheiling and its merry band, Neil MacLeod writes:—

'N am an cruinneachadh do'n bhuailidh
B'e mo luaidh a bhi 'nan còir;
Bhiodh a duanag aig gach guanaig,
Agus cuach aice 'na dòrn;
Bhiodh mac-talla freagairt shuas
E ri aithris fuaim a beòil;
Ach cha chluinnear sin 'san am so
Anns a' ghleann 'san robh mi òg.

When the lassies gaed a-fauldin',
Aft I joined the merry thrang,
In their hands their milkin' coggies,
An' frae ilka voice a sang;
While the echoes sweet and clear
Wad gi'e answer frae the ben—
But we hear nae mair their liltin'
In my bonnie native glen.