So I knat-up a replacement.
It's leftover blue wool from the skein Veronique sent me last year (which I used in a hot-water-bottle-cover for my mother). I made it in a similar style to the PDA case I did a while back. Turkish cast-on, in this case about 80sts, and worked in st st round until about twice the desired length. Then folded back in half (so worked row is level to cast on one) and kitchenered shut. This gives a nice double-thick piece with neat lip to the purse. Then put it in the wash for a hot, fast spin with a pair of jeans and a towel or three. Sew on zip, work a bit of random embroidery. Ta-da!
I kept with Veronique's mix of this blue with a dark chocolate brown for the zip and decoration. None of this especially goes with my red glasses, but we'll ignore that.
All so much nicer than the black logoed plastic things they give you at the opticians. I don't know why it took me so long to make one.