Perhaps I did not word it well..
That Lusitania carried cases of Remington made .303 inch ammunition for delivery to the British is well documented, Remington also had a contract to manufacture bayonets made to the English enfield 1907 pattern. Perhaps these were also being carried by Lusitania on other early 1915 crossings, or maybe even the final May voyage.
As far as I have been able to determine, production was well established in the months before the sinking. So they must have been shipped across on various vessels, since Lusitania was carrying ammunition also manufactured by the same company it seems possible that bayonets may have also been carried aboard at some point.