That's the#1 question I get in my inbox. Other versions are, "Why are the waist sizes on all your 50s dresses so tiny?" or "My measurements are 36-30-37 (or 42-37-44, or 39-33-38). Do you have a 50s dress that will fit me?" In fact, I get this question so often, I am going to address it here for all of you who have been frustrated in your search for an authentic vintage dress.
The fact of the matter is, the industry standard for measurements in the 1950s was a 10" difference between the bust and waist. That means if you find a dress with a 36" bust measurement, 9 times out of 10, that dress will have a waist that measures 26". If you don't have a waist that is 10" smaller than your bust (and believe me, most of us modern women don't), that explains why you're having a difficult time in your search.
So what's a gal to do? Here are some suggestions to help you overcome the obstacles.
#1 - Consider foundation garments.

#2 - Consider separates.

#3 - Consider a dress from the 60s instead.
By the mid-to-late 60s, women were moving away from wearing a girdle at all times, and styles moved to a more relaxed waistline. If there is a 6" or less difference between your bust and waist measurements, your body type may be more suited to a shift or empire waisted style from the 1960s. Try it!
#4 - Have a dress altered to fit you.

#5 - Sew your own or have a dress custom made.
Most of the major pattern companies now offer modern reissues of vintage styles. And vintage patterns abound on the web. If you can sew and know how to alter a pattern to fit, making your own dress is a great option. If you are going to use a vintage pattern, you'll likely have to know how to grade the pattern up or down to fit your size. If you can't sew, find a good custom dressmaker in your area to do the job for you.
I hope these suggestions help you in your search! If you have another to add, please post it in the comments!