Indirect Material - No Material group & no material master

Hi,

Please help me in the below query

my client is having many indirect material - they are not maintaining any material group / material master.

they do P2P process as below

1. PR will be created in non sap system - through Functional Module (FM) it will be pushed to SAP system

2. PO will be created automatically in SAP system

my query is in the above case, how to bring the tax code into PO automatically.

Kindly help me in this regard.

Thanks in advance

Lee