The singer was Memphis Slim. It is avalible on a CD called "Bawdy Blues" on Prestige/Bluesville Records. Most of the song is a spoken monolog and I'll try to transcirbe it tomorrow. The chorus is sung, a 12-bar blues:

If You See Kay

If you see kay, tell her to come back home
If you see kay, tell her to come back home
I ain't had no lovin since that gal been gone

and it ends:

So remember to contact Memphis Slim
If you see kay.