I have had several clients recently need grips to go with their restorations, some had VOPO grips or other cheap plastic or really bad grips they did not want to keep. I sugguest first checking with Lugerdoc or Hugh Clark for them, Hugh can usually supply checkered or smooth grips or specially made checkered ones with a smooth border like some of the very early commercial Lugers had. A current supply of Nill Walnut grips is MacTec
http://mactec-militaryarms.com/
Factory authorized dealer / importer of KN Nill Grips
These are the very best replacement walnut grips IMO.