In an early post we have a look at the vendor auto add. If category is too narrow to search or you want a shorter list of vendors then you can use the vendor search. It works or attributes that you might flag on the vendor like minority interests etc. You can then use these to filter. Which will come up with a short list and you can remove vendors from the search list before adding to the line.
Here is a quick overview.
AX2012 R3 CU11