Adam:
It depends entirely on how you count: by firms or by individuals.
The ASGCA list includes several people in the Fazio and Nicklaus firms [but it also does not include a lot of their younger, on-site people]. It leaves out any architects not in the society, including everyone in my firm, others who have chosen not to join, "golf planners" working for a landscape architect firm, and a lot of young designers with only a couple of courses under their belts.
If you include all of them, there are probably 200 "design companies" you could hire today.
My guess is there are as many as 500 people in America drawing some sort of pay as a golf course architect or associate. On top of those, there are 50-75 students who apply for our internship each year [I'm sure we don't hear from them all, but only maybe 2/3 of those we hear from are really seriously pursuing a career to the exclusion of other aspects of landscape architecture] ... and there are a lot of graduates working in construction or other venues and hoping to catch on with an architect.
Which is a very long-winded way of saying the supply is much bigger than the demand.