Halloween costume shopping

So,
I always like to dress up for Halloween, yes, I am an adult, but I've always liked to create unique costumes and really get into the Halloween spirit. One year I was the bride of Frankenstein, and it really freaked my son out. There is a really cool store in a town near here (Mt. Horeb, WI), called "Vibe". They have clothes from the 30s thru to today. Lots of really cool 50's and 60's dresses. I thought for sure I could find a costume there. I found one really cool green dress...I don't know what it was from, I think the early 70's. It would be perfect for me to go as Mrs. Brady, a little blonde dye and I'd be fine. Well, that dress was tiny around the waist. So I tried on lots of different dresses from the 50's, 60's and 70's, and NOTHING FIT. Just around my arms and shoulders, not to mention my chest. I guess people were much thinner in the 50's, 60's and 70's (these were authentic clothes). I guess it's no surprise, since there is a McDonald's on every other corner. I was disgusted with myself, and embarrassed that I couldn't find anything to fit.
Now I'm not into Halloween at all. Maybe I should use this as motivation to get moving.