"Defunct graphics chip makers" is correct, as would be "defunct graphics card makers."

Graphics is plural because, as a general capability, there are not only many different aspects to rendering graphics (drawing, rendering, shading, etc.), but also there are almost always multiple graphics that must be rendered and displayed on a computer screen at any one time. Thus, "the graphics card," "the graphics chip," "the graphics engine," have each become standard.

Interestingly enough, if you were to say "makers of graphics chips," "chips" would, in fact, be required to be plural. The only exception would be in the case of the makers of a specific kind of chip, as in "the makers of the XYZ-9000 graphics chip." But you could equally say "makers of XYZ-9000 graphics chips" and be equally proper. Although, to some, perhaps many, this might imply that there is more than one manufacturing company making these chips and that the XYZ-9000 is, in this instance, a 'generic' reference or standard, such that we are not talking about a particular, branded component anymore. To be sure, at this level, we are splitting hairs, but vagueness like this is in fact the kind of thing that branding and trademarking specialists do find themselves worrying about.

However, in the case at hand, the grammar works the way it does for cars, bagels, and drugs, as in: car makers, bagel makers, and drug makers. Thus, "graphics chip makers" is the correct form.

For another analog, consider the word "analytics," as in "analytics software engineers," "analytics code authors," or an "analytics module developers" -- same basic thing.