In some sort of strange synchronicity, I was reading about the minimalist painter Agnes Martin and her being described as an "art nun" and probably being asexual-looking at some of her paintings I cam across this from 1959!
On a similarly arty theme, in the current Queer British Art exhibition at Tate Britain there is a painting of Dame Edith Sitwell. The caption mentions that she apparently didn't have any sexual relationships. The longer entry in the catalogue has the word 'asexual' (not specifically as an orientation but that she'd lived a seemingly asexual life, or some such wording). It was nice to feel that there was a tiny bit of representation there, although there was also a festival going on relating to Pride when I was there that didn't include asexuality at all. I guess you win some, you lose some!