Dear Steven,
I came to the same dilemma and wonder if the Taiwan or Beijing Museums have some in storage. Cloisonne snuff bottles were rarely collected until the last 8 to 10 years. The main reason was the fact that so many reproduction were made since the 1950's. Most dealers and collectors put all but a very few in the category of tourist trash.
I am wondering where you found the date "1789" for a closing of the Imperial workshop? I have the catalog "Cloisonné - Chinese Enamels from the Yuan, Ming, and Qing Dynasties" from the Exhibition held at the Bard Graduate school January 26 – April 17, 2011
https://www.bgc.bard.edu/gallery/exhibitions/27/cloisonnIn it they have a chapter dedicated to the Imperial patronage of the arts. It explains that there is very little written record pertaining specifically to cloisonne, but from the records they list "workshops and manufactures in the province of Guangdong, in the cities of Yangzhou (Jiangsu province), Beijing (Heibei province), and Jiujiang (Jiangxi province), among others, each of which displayed different styles and characteristics."
They do not mention the closing of a specific location. I would be interested in your source.
Incidentally in reading that chapter again, I found the following to be very interesting. "The archives reveal that after the thirty-third year of the Qianlong reign (1769), the Hongli emperor often commanded that double gold-plating be used. For these reasons, the cloisonné objects of the Qianlong period are for the most part brilliant and glittering; ..." and "After the Jiaqing era, the production of enamels by the Imperial Manufactures decreased, doubtless because of domestic problems, foreign invasions, and China's declining power." Personally I would add that the Daoguang Emperor was somewhat obsessed with the style of the Yongzheng period and Yongzheng didn't order much cloisonné preferring painted enamel work.
Best regards,
Tom B.
