You are so lucky. At 5'4" I can never find bikes in my size to test ride. Bike shops carry 54, 56 and 58 but not 49 or 50cm with any regularity. If they do, it's only the aluminum models, never the carbon ones. I've ridden a 49cm Allez for the last 18 months, which feels like it's fit decently to me. However in a year or three when I'll be looking to upgrade to a carbon bike and there won't be any way for me to test ride them. Which will likely end with me riding a Tarmac, as it's essentially the same bike as the one I'm riding now, just in carbon.
I guess your issue is that bike shops don't want to manage inventory one bike at a time; if they order a bike for you, they want to know you will buy it. But will they let you order it if you want to buy it? I think a lot of them do. So the only issue is that you need to know if you'll fit a particular bike. I know it's not ideal, but maybe go get a fitting done with some recommended measurements, and then order a bike based on those measurements? Not sure, create another thread about this and see what the more knowledgeable people here can advise. Good luck!