Not easily done now that 2015's are out. Inventory search won't let you specify options on 2014's. Even dealer's websites don't always list all the options on a given vehicle. The only way to be fairly sure is to load window sticker for each one that's close to what you want. That's how I found mine. Laborious at best. If you're working with a dealer, he may be able to search for your desired options in existing inventory. Good luck !
I found mine (black, dual sliders, rear glass, glass in both sliders, heated seats, backup cam, uconnect, and more by searching cars.com. You can do an advanced search and pick a color or search the entire country by keyword. For example, I did "left rear door " or "drivers side slider". I don't remember the exact phrase.
I also did the same on autotrader.com, but it was more difficult.
cars.com, autotrader.com, commercialtrucktrader.com, carsforsale.com, searchtempest.com (for craigslist nationwide), ebay.com. You should be using all of these. The problem is not all dealers post their inventory on these sites so don't only rely on them. That's why you need to contact a fleet manager to run a search of all Promasters in your area.