I have a couple of old 'Sears' and screw-mount lenses lying around that I don't have a use for - wondering if there is an achromat in regular lenses that might be of use?

Achromat lens scheme is one of oledst. In very early times those were in production as full functional photolens. Now it is part of more difficult schemes. So it's true You can find those from photolens.
You have to study just diagram of Your lens. If You don't know how achromat looks in diagrams, then here You can find diagram of Achromat (http://en.wikipedia.org/wiki/Achromat)