The phrase "are produced at a" is correct and usable in written English.
It can be used when discussing the location or context in which something is created or manufactured.
Example: "The finest wines are produced at a vineyard known for its unique terroir."
Alternatives: "are created at a" or "are made at a".
Because all new television shows are produced at a deficit, ABC is promising to accept all those initial losses.
Superphosphates and sulfuric acid are produced at a plant on Cockle Creek, which enters the lake from the north.
The 500, 500C and 500 Abarth are produced at a plant operated by Chrysler, Fiat's corporate sibling, in Toluca, Mexico.
About half of all consumer electronics sold in the world today are produced at a single mammoth factory campus in Shenzhen, China, according to Mr. Daisey.
Colman's products, including its famous English mustard, are produced at a factory in Norwich, while Elmlea, the cream alternative made from buttermilk and vegetable oil, is produced at Unilever's food factory in Purfleet, Essex.
Many hormones are produced at a relatively constant rate, and in healthy individuals the day-to-day serum concentrations of these hormones lie within a rather narrow normal range.
The show is a love song to Apple's gorgeous, transformative devices, but also a vehement attack on the way they are produced, at a vast, dehumanising factory complex in southern China, where workers assemble laptops and smart phones for next to nothing, under constant surveillance.
As far as I know, Red Bull and GoPro videos are produced at a loss.
The uninfected hepatocytes are produced at a rate (lambda^{alpha}) and die at a rate (d^{alpha}).
(The show's secondary segments, involving the team of Kari Byron, Grant Imahara and Tory Belleci, are produced at a different location).
