I'm with kuduae--it's a stock bolt handle at an odd photo angle. Bill--there seems to be an odd synchronicity to the availability of these things. Sometimes you'll see a whole rash (well, relatively--say 3 to 5) of one particular model for sale via different web sources over the span of a month or so, then nothing for 6 months. It was that way recently with the M1910. On the other hand, the scarcity directly relates to the level of workmanship and time and skill it took to build these guns. If they were more common, they'd probably be a lot less interesting!
Best,
Malcolm