No I don't; but the evidence they were made is documented in the excerpts given above by "Martin Gibson".

In the book "Gibson's Fabulous Flat Top Guitars: An Illustrated History & Guide" by Eldin Whitford, David Vinopral, & Dan Erlewine published in 1994 by GPI books, the only J300 model made by Gibson is described as follows:

"Two other models, both offshoots of the basic J-200 came out of the Kalamzoo factory in that decade. The J-250R produced from about 1970 to 1978, was a standard issue J-200, but with rosewodd back and sides.

As far as Epiphone goes, I have no information other than they were not part of the Gibson organization until they were purchased by Gibson in 1957.

The second model, the J-300 Artist, proved a more interesting variation, although it lasted only a year after it's introduction in 1970. This striking guitar, also with rosewood sides and back, differs visually with its delicate, fleurs-de-lis gracing outside of the bridge; the lower bout of the pickguard, and the peghead. Sadly, this J-200 upgrade sold too poorly to justify it's existance."

And by Cluin:

Gruhn's Guide to Vintage Guitars (published 1999), which I borrowed from the library today:

J-300 Artist:
17" wide
rosewood back and sides
J-200 bridge and pickguard
fleur-de-lis peghead inlay
Available: 1970-71

Sorry we don't have more to offer.

A