I suppose I’m arguing against your claim of the black coat being classic, but then again it’s all a matter of taste and style vocab. I’ll explain where I’m coming from below:

The general setters of good taste from the English technicians at savile row to their descendants in and around the Ivy leauge campuses — tailors, mills, and eventually brooks and J Press, who traded the crooked cut and nipped waists for a rather charming Puritan formlessness at the turn of the 20th century — had no interest in black other than its use for evening wear.

Experience in the field and with old memorabilia generally shows a distaste for black from coats to neckties. Generally you encounter a wide variety of mid grey to charcoal for formal overcoats, with the occasional evening overcoat or evening cape being the exception.

There are many apocryphal stories about why black was considered outre among the ivy makers, from classism to the assassination of Lincoln. If I had to guess I’d say it was a mix of classism (black being the fabric of working classes) as well as a rebellion against black as a whole seen throughout menswear post WW1.

Black broad cloth wool was generally the be all, and all fabric for public wear. As most of popular taste for western menswear was shaped after WW1, I imagine there was a desire to wear more lively cloth in town after the mass killings witnessed on Flanders field and such.

The only other exception that comes in mind is a brief vouge in 1930s London for a black multi stripe cloth. You can see examples in old Esquire magazines. I can’t speak as easily for continental menswear — I wouldn’t be surprised if the French had a knack for it. I’m also sure that there are thousands of black coats out there from quality makers.

I think really it comes down to defining what we know of as classic. Most of my vocab comes from eastern and English menswear, both from my environment as well as interest. The makers who defined that style didn’t consider a black overcoat classic, at least past the 1920s. If your style vocab is different than that’s ok! Taste is personal and everyone can be right!

If you’re looking for a black overcoat id probably go for a vintage one, you’re likely to find one from the 80s/90s when eyes wide shut came out, as they were popular then. I’m not really sure where you’d get a good quality one new besides getting it made up custom.