There's a couple ways into this field. With industrial or office businesses, about a third of the major decisions are aided by a small group of site consultants. Bob Ady is the "father" of the field, and is still practicing. Colliers, Deloite/Tuiche, NCS, Anderson, Ady International and a handful of others are the big players, but there are dozens of smaller ones. Many of them attend the International Economic Development Council's annual conference. I usually make it a point to go out to dinner with a few of them. The conference will be held in St. Louis next year, and if you go, you are welcome to join us. The bad news is that these are people with extensive experience in real estate, economic development, and accounting. You can't simply start out in the field after graduation.
Many retailers have site selection divisions. I worked in one for a short time, just as I was finishing my masters. It was not a pleasant experience. Ostensibly, I was hired because of the research I had done on the use of GIS in retail site selection. I never even saw a real GIS there. My job was to fly out to the site, drive around the neighborhood to get a feel for it, case the competition, take pictures and fly home. Back at the office I would mark up a site plan, put dots on a paper map to indicate the site and competition, and plug some numbers into a spreadsheet. Then I filled in the blanks on a four-page site report. If I make this sound the sort of boring, routine work that requires no thought, I'm probably not painting a dismal enough picture. A bachelor's degree is all that is required, but a masters helps.
I went back to economic development. Now I work to market the community. I am in an organization that has been developing its own 560-acre business park. I get to work with businesses who are looking for locations, trying to convince them to come here. Today I met with developers looking to redevelopa property as a shopping plaza. I will work with them on the design, facilitate the permits, and help them to recruit stores. I have also developed six acres of commercial ground nearby. There are a few entry level jobs in economic development, but it is also a field that is easy to move into from planning.
I guess what I am suggesting, is maybe you want to check out economic development. Planners (especially those who understand business) make very good economic developers. Here's another perk - while planners usually end up in the basement, the economic developers usually get the corner office. Mine has a fireplace.