Your post doesn't have enough information. I'm not sure if you're referring to Ardmore, Pennsylvania, but that would be something you would have to google yourself to find out as I'm not familiar with stores everywhere around the nation that can do that sort of thing.
Try googling a dry cleaner in your area that specializes in wedding dresses.
But to answer your question about converting a prom dress into a wedding dress, a FULL conversion couldn't be done without compromising fabric integrity. Consider using material from your prom dress to create a sash, veil or even a garter. Beyond that, changing a dress' color would weaken the fabric too much.