I think this may be a variation on the BrE expression "for two pins", which means:
At the slightest provocation; for the smallest reason.
Farlex Dictionary of Idioms (via TFD)
I assume that "pins" here refers to the type used in sewing or another practically worthless type of pin.
The earliest attestation of this idiom that I found so far is from 1890:
For two pins I'd put a match in every gunyah on the place.
The Squatter's Dream: A Story of Australian Life
Here's another early example from The Times (London, 1794):
I'll blow you up for a sodomite, for two pins.
There are other, older idioms where pins are worthless (note that the expression most likely refers to pins made of wood or bone, not metal). "Not worth a pin", "wouldn't care a pin", etc.:
He seide al þat he had ywonne
Jn þe werlde vnder sonne,
He nolde ȝiue þere-of a pynne,
Bot he miȝth þise wynne.
He said all that he had won
In the world under the sun,
He wouldn't give thereof a pin,
If he might win this.
See 9. b for more quotes (and a definition) from Middle English.
It was even used by Shakespeare:
A round hose, madam, now's not worth a pin.
The Two Gentlemen of Verona
It's worth mentioning that I found the exact same expression "for a couple o' pins" in:
- The Leisure Hour (1904):
[F]or a couple o' pins I'd shteam-rowl yez under the two feet o' me.
- The chimney corner (1879):
See now, for a couple o' pins I'd take both yerself an' the little sweep ye call 'John' to the lock-ups!