I just bought some from HPSI Motorsports, they are in Oklahoma so I'm partial to them, I wanted 3.5mm but went with what they had which was 3mm. It works fine. I wanted to replace all my vacuum hose so I went ahead and bought 6mm, 8mm, & 10mm. That covers PCV, Evap, brake booster and most anything else that I could measure. This is on my 98 Montero so YMMV.

1998 Montero (CW Pack)
1979 Chevy LUV 4x4
2000 GMC 2500 4X4