You're welcome, yep, Berlin, Steel Vintage Bikes has done a number on the market there and in general so very few good deals to be had and these are that way to begin with so you will have to temper your wants, needs, expectations and reality accordingly to get there.

You are in the right place although "mixte's" and such present a unique challenge as you are finding out.

531 is especially challenging despite being used extensively in quality and custom builds they are still quite rare and will not be cheap even if you can find one.

I encourage you to raise your ask some and lower your expectations some to get you there. You should be able to find a Japanese version made with Tange and many of them are excellent quality and very, very well made as well as beautiful too.

One more thing to add, part of altering expectations will get you there sooner, too stringent and you may never get there.

Dig in, get something to start with and work through the process, you can have a very nice placeholder that will foster better thinking moving forward so you may be able to capitalize on something you may not have considered otherwise.