These are primarily offered on eBay by a Malaysian seller of antiques from Borneo. This seller has a 99.6% positive feedback rating.
Supposedly, these miniature crocodile-shaped cannon are 80-100 years old, and were once used "as currency" in Borneo.
Whether or not any of this is true, I can't say. A lot of items were produced solely for trade in those days, it's not outside the realm of possibility that these were once desirable to some in the import/export business. And if that's true then any value they might have as cannon is secondary to their curio value.
That said, I still think the BIN price of $1600 US (plus a hefty shipping fee) is ridiculous.
FWIW : This seller also lists antique bronze swivel guns.