When you say Vintage do you mean one from the 50/60s if so you are , then you probably need to be no bigger than a size 12 as sizing was very small back then as ladies tended to be slimmer and shorter than they are now, does anywhere in your area have a good quality used dress shop? They usually do mother or the bride / groom but will often have evening gowns too also if you ask in Charity shops they often have some out the back rather than on display so they don't get damaged / dirty. I find travelling a bit away from your home town to some of the more " posher" areas often have a better selection in their charity shops. Also online hire agency are becoming a big thing with even M&S getting in on the deal .The only thing with hiring online is you don't see it till it arrives and if it doesn't fit or you don't like it you would be a bit stuck.