Or sacrifice a set of plastic keys - trim the tops to, say, .25", then drill a blind hole in the wooden key, a bit of glue, and there you are. Alignment would be a pain, but wouldn't take as long as carving the keys.
On that, there are CNC machines for wood - they might be a good option. That, or get a small mill and a good vise, and make some jigs for the basic shaping. Keys are a fairly complex set of curves.
Third idea is to get a set of keys in orange or yellow plastic, and paint them with a 2-in-1 stain and sealant, to get a woodgrain effect. Engraved letters should still show through, or you could go for the blank style.