Do a search via google, we regularly discuss where to find vintage bikes. Lots of places outside ebay and C/L. You will find 500 to 1000 discussions on this topic with lots of good opinions.

The more specific you get (model, size, color, era), the more likely you will have to be extremely patient and ready to pay at or near full value. My most recent personal builds, framesets, were both picked up on ebay, not the cheapest method for sure. But I wanted an exact model, color, year, and size. And they both were only offered one year.

On other personal bikes, I was open to brand, year, but choosy on size. I got better deals on them.

Google search this forum on how/where to find bikes, rather than a bike to buy. Bikes to buy are in the marketplace.