I was browsing through some older threads this snowy cold morning and found this thread that is over a year old that I somehow missed the first time through. I wanted to comment on some mis-information that if not corrected, just keeps being repeated as fact. The OP's original research is very accurate in where these bayonets were made, but I just wanted to expand on it a little if I could.
These bayonets were not made for captured T-38 or T-99 rifles, nor were they imported in with the batch of rifles from China in the late '80's - early '90's. I suspect that the OP's "serious collector friend" might have known what this bayonet was and since he offered to buy it, was just trying to take advantage of the OP's lack of available knowledge of this unknown bayonet.
These bayonets were made in the Tientsin area in China under Japanesecontrol. They were made for the Type-19 Carbine in 6.5mm and the "collector defined" North China T-30 Copy in 8mm mauser. There were 3-4 smaller factories in this area that made these bayonets along with the Tientsin Arsenal, but the Tientsin Arsenal was the final inspector for them. There are small differences in each factories examples such as grip and pommel shape, serialized vs. unserialized and scabbard configurations. The muzzle ring inside diameter of the bayonets will range from 14mm - 17mm. The 6.5mm barrel of the T-19 Carbine measures 14mm and the 8mm T30 copy measures 16mm. The known serial number range of the OP's bayonet is 241-1174 and is considered a rare bayonet! This information has been known for close to 15 years.
Aragorn243.... you have a great bayonet there with the proper scabbard!
Hope this has been helpful!