One excellent source for buying vintage glasses is Etsy. Most people know it as a website for handmade crafts and jewelry, but the vintage hunter can also find much to love here. When searching for vintage eyeglasses, just set the search drop-down to “Vintage” (the default is “Handmade”), enter “eyeglasses”, and browse away.
Many of the Etsy shops selling vintage eyeglass frames do not specialize in eyeglasses, but offer an assortment of vintage odds-and-ends. A few shops, however, focus exclusively on eyewear. One of the most extensive is Vintage50sEyewear, which has an excellent selection of cat’s eye frames, often embellished with rhinestones and beautiful engravings and mostly priced between $40-$65.
When considering an Etsy purchase from a shop that does not specialize in eyeglasses, make sure the seller indicates the measurements of the glasses, so you can be sure they will fit, and whether or not there are prescription lenses in them already (as getting your own RX put in will be an additional expense).
Some other Etsy shops with a good selection of vintage eyeglasses:

Do not buy from Aubie Jean Vintage. Packages are not shipped despite receiving payment from buyer, does not forward tracking numbers, lots of run around. Completely not trust worthy,
Thanks for your comment, Nancy, and I’m sorry you had a bad experience with that shop. I’ve never bought anything from there so I have no experience to relate. However, I note that the shop has a lot of feedback and most of it is positive.