He rates a Wikipedia entry: Wikipedia - James Ruse, which qotes the epitaph among the other information.

The words appear in a song file of the Cornish Association of NSW CANSW Song Sheets (Adobe pdf file), where the author is listed only as Gendall. You might be able to get more information from them.

Below is the song as it appear there.

Mick

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James Ruse (Gendall)

James Ruse is my name, and from Cornwall I came,
A husbandman born in times that were poor.
Two watches I stole and a few shillings more,
And for this was sentenced to seven years
Far, far, far from my own native shore.

(Refrain)
My mother reared me tenderly, with me she took much pains,
And when I arrived in this colony I sowed the first grains,
and now with my heavenly Father I hope for ever to remain.

They put me aboard of the 'Scarborough' then,
And off to Australia with many poor men,
Across the two oceans we zigzagged our way,
With good Captain Phillip a-sailing,
Far, far, far to Botany Bay.

"I'll give you a garden James Ruse he did say,
"And thirty more acres if you'll make it pay."
So I sowed the first grain in this far distant strand,
And when it was ripe a first harvest I
Saw, saw, saw, in this far distant land.

O' many the troubles that I had to bear
From drought and from flood and hard labouring fare;
And I wed Lizzie Perry down under, to share
The first farming country that ever was
Here, here, here in this hot dusty air.

And now I do lie in St. John's Campbelltown,
Beside my good wife in Australian ground...
We had a good life, but I'm proud to proclaim
I was the first gardener and husbandman
Here, here, here in this distant domain.