Hi Adella,
Large size feminine shoes can be hard to track down.
Finding them at a bargain price is very difficult.
I too wear a Euro 48 in Birkenstock sandals and US Men's size shoe in the range 14D through 15E depending on the manufacturer. I shop on the internet for all my shoes, as I have not found any retail stores within 300 miles of Portland, Oregon USA that stock my size in Women's shoes.
I have had good luck at
http://www.barefoottess.com/ You can filter by size and they often have 15 and 15W shoes that are large enough. Most styles will have a "measurements " tab that is very helpful in determining which styles are running large.
The styles they have available change multiple times a year, so you have to keep checking (today, the selection was very limited, the most feminine were a couple of large Wedges.
The best bargains are when they have a 30% or 40% off sale.
You may want to check out
http://www.shoesofyourdreams.com/They are a bit more expensive, but often better than a many of the internet sites that specialize in feminine clothing in men's sizes.
PS Sorry for the slow response, I haven't had time to to keep up.
-Cindi