Actually, BMW make a kit of needed rivets for their old set of locks. All the size and length needed are in the kit, so you just have to select the correct one.
If you already have a bunch of rivets, buying the kit make little sense, but if you do not have any but the rivet tool, this is the way to go.
BTW, a friend of mine repaired his suitcase using epoxy resin and glass mat cloth. He did a fine job of it and once painted black, difficult to see.
Forgot the BMW P/N : 46 54 9 057 696