After the war in China really started to escalate in 1937, there were several factions of Chinese troops who were loyal to the Japanese in the areas that were controlled by the Japanese. The captured weapons were only going so far to arm these puppet troops, so the Japanese went to the Arsenals that were in their territory and started production of various types of weapons to outfit these loyal troops, mostly the T-30 copy in 8mm and T-19 carbines. Production of these two types of Carbines combined is believed to be around 70K.
So to answer your question, these rifles and bayonets would have been used against the Chinese communists forces and I assume possibly the Soviets in the North.
On the low production number of your bayonet, remember there were I believe at least 4 different factories producing these bayonets with their own serial number blocks to fill. Some bayo's have no serial and some have higher serial numbers. But taken into account where all of these rifles and bayonets were used, in China, makes sense why they are so scarce here today.
A fantastic reference book "The type 38 Arisaka" written by Francis C. Allan goes into great detail on this part of Japan's war against China.