Jameco had a good selection of different perf board
shapes,
sizes and materials. Not cheap but a good selection. They
ship really fast. I live in the bay area and usually get my
order the next day if ordered before noon the day before.
If you need specialty board, such as for a older PC or
S-100 try Anchor Electronics. They have these things
as well.
These boards are cheap enough in Brazil, but I'm planning to do some
"speciality types" when I put my cnc machine working...