I wouldn't want to speculate as to the actual percentage of households with enema equipment, and even there, whether or not the equipment sees relatively regular use would be a factor,
but I would bet that the percentage has been increasing, probably for at least a decade .... and likely longer
My reasoning:
(1) aging of the general population, coupled with lower incomes and the "new frugality" which emphasises less-expensive living
(2) greater interest in alternative health, which often reccommends use of enemas, and has a built-in suspicion toward disposables
(3) a general weakening of the "psycho-sexual" taboo against the use and mention of enemas
(4) diminution of the AIDS scare; back in the eighties, some syringes, particularly the folding types sold mostly to single women, even omitted the rectal pipe from the package
So my guess is that use of the enema has become somewhat more common, but still not on a scale as great as the 1930's-50's. At one time, there were reference sources, such as the Thomas Register, which listed the production of "rubber goods" in the United States from year to year, but I'm not sure this would be the case today with the products now produced overseas.