Billy McComb has three books and a number of published manuscripts.
The First Book of William, published in England around 1946 is long out of print.
25 Years Wiser was published by Supreme circa 1972, his biggest and a hardback should be available from Magic Books by Post in England (search under google).
Recently Martin Breese republished The Professional Touch which is basically a series of audiotapes in book form - and detailing first class professional routines.
Billy himself has published a series of manuscripts, each routing one effect from his professional repertoire. I don't know if they are stocked by dealers but are available from Billy at lectures.
If you can get access to back issues of The Magigram, Billy started an irregular monthly column in 1972. You can also check out in those Magigrams the monthly columns of Billy's cousin George Johnstone.