there's been a handful of companies...
...some are still made today. I know that Girard Perregaux has a Cloisonné artist on staff. JLC makes enamel pictorial dials (that is, not just showing numerals but an actual handmade scene) and I believe Patek will do so on order, however, I believe they are technically less complex than Cloisonné which uses wires to inlay the powders.
When I asked GP whether they did it "in-house", even having the oven and the haute horologerie person there said "sure but the oven is a little larger than a shoe box, that's all".
From the 1950s, I've seen several dials by several companies, also including Vacheron as well as Patek and IWC. They all look surprisingly similar and I've always thought that one third party supplier sold each of the companies on his Cloisonné work. To my thinking, IWC's historical Cloisonné dials are as good as any.
Regards,
Michael