Unfortunately there is no way to do this type of search in the Vault Manager search facility as a target value always has to be specified.
The way to approach this would be to list all parts ordered by the attribute 'order code' then scan the list looking for adjacent duplicate 'order code' values. Although the Vault Manager search allows ordering by user defined attributes it doesn't at present show those user defined attributes in the resulting "Vault Items" grid.
The PDC Vault interface would allow this type information to be shown, if you have a PDC license
This kind of list could also be generated using the Postgres "PGAdmin |||" utility but you may not be familiar with that tool either.