Searching through old club publications:-
The pad for the normal 72-73 Type 3 and 411 caliper is the same as REAR pads on all 75-90 Volvo 240s, says Per Lindgren, Norway, who should know as he has a 73 Variant L.
GSF seem to have them; look at Volvo then brake (actually looks like '78-'92 though). http://www.gsfcarparts.com