Your wives by you gifts from the merchants in your area. The gift can be anything from a carrot to a master weapon.
In the Case of Lady Grey she lives in the area where the Solus sword is sold so The chances of her giving you the Solus is one in.... however many items the merchant has. So let's say..... 1 in 100. You can increase those odds by buying everything else the merchant has and then hoping that she is happy enough to give you a gift soon, but there is NO FREAKING POINT TO THAT! You are better off just buying it yourself! especially given how wonky Lady Grey's wife AI is.
http://www.myspace.com/phoenix_corp_ceo "You are a planned organism, the offspring of knowledge and imagination rather than of individuals"-Morpheus