I get the BusBoard ones, from Amazon
Amazon.com: ST1 (Two-Pack) StripBoard, Uncut Strips, 1 Sided PCB, Size 1 = 50 x 80mm (1.97 x 3.15in) : Industrial & Scientific
Obviously other vendors sell it too. ST1 | StripBoard-Size 1 | BusBoard Prototype Systems
I've also bought the stuff Tayda...