Looks like a Turkish M1935, as used on Mauser 1893 and 1903 rifles in 8mm. See http://worldbayonets.com/Bayonet_Identification_Guide/Turkey/turkey_2.html
The scabbard is wrong though. If you follow the link, the scabbard looks like the one used on the M1935 bayonet modified for the US M1 Garand rifle. The bayonet itself is clearly not modified, so I suppose somewhere along the way somebody swapped a newer scabbard onto the older bayo.
There are a few on eBay, asking prices appear to hover around the $50 range.
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