here is a chart for how strong metric bolts can be and their gradings.
http://home.jtan.com/~joe/KIAT/kiat_2.htm
for getting bolts, you probably can find a specialist in your area or go to
http://www.mcmaster.com/#
and GEEEEK out and order.
remember 10.9 = about a grade 8 , and 8.8 = a grade 5. -- so very very few places on the car will require a 12.9 grade.
--Steve