A family member of mine has an old P08.  He'd like to put a set of replacement wood grips on it.  Does anyone have any suggestions where he could find some good replacement grips?

We need more information on the specific P.08, and what your goal is.

1.  If you just want a set of new checkered walnut grips for a P.08 Luger you can find them on Amazon for about $30, although some variants may require minor fitting.   Gun broker is also an obvious place to look.

2.  If you want a period correct set of grips, it depends on when your P.08 was made.  For example WWI era P.08s had checkered walnut grips, while WWII production P.08s began using black plastic grips around late 1941.

3.  If you want grips that add value to an otherwise all matching number Luger you'll need to find a set that are both period correct and have the last two numbers that match your Luger's 4 digit serial stamped on the inside.  That's why they list the number on the grips on Gunbroker, and why a pair of matched, numbered grips can be so expensive.
 
This is an all matching number 1918 DWM P.08 Luger:

Thank you for your input.

This is a 1913 (I think) Luger.  He just wants another cheap set of grips he can shoot it with so he doesn't mess up the original grips.  I'll refer him to one of the $30 sets.  Thanks!

Unless you find a set of East German VOPO grips your only option is to buy Nill grips. They are not cheap, but were OEM for Germany in WWII.

OEM like in original equipment manufacturing? Karl Nill started his shop in 1969.