From what I know,

100f is discontinued in all formats globally, but is still available at retail
50 and 100 received a package redesign this year and are still available in Japan in 4x5 and 8x10
Only 100 is available in 4x5 in North America (no 50) - check Adorama they have 100
50 is still available everywhere in 35mm and 120
5x7 Velvia is discontinued but available at retail in Japan

Hope that helps?