After I got to Guam, I didn't find much in the way of film. As Mustafa pointed out above, it seems very likely it's shipped in from the US. I found some Kokak negative film in a supermarket, that was it.
A follow up on the cost of Velvia 50, I just bought some for an overseas trip. It now costs 18,000 Korean won for a 36 exposure roll, that's $16.77 right now according to xe.com. I'm flying to Nepal tomorrow, it was not good being in a shop having to calculate how much film I could afford to buy for the trip. Last time I stocked up on Velvia it was sold in packs of 10 - it's now sold in packs of 5.