Seriously there are not many convex knives around there and those who are are generally handmade so a bit expensive.
Opinels are great and you should get one but not so sure they can speak for all convex grinds, they are so thin actual shape of blade is hard to tell and the angle is such it is hard to tell convex from flat anyway.
Maybe Condor knives have so fairly cheap convex.
Also Valiantco blades have a nice full convex and some are quite inexpensive (prices are in australian dollars).
I've also had some very inexpensive Filipino blades from ebay: full convex, nice grinds but steel/heat treatment was really awful.
I'd say try to reprofile a knife by yourself.