I advise you to get a solicitor and they may help you get in touch quickly with UKVI. What you need to do is to keep on contacting and getting in touch with UKVI. Try everything you can. UKVI states that they can replace a lost visa especially if you have documents to support that your wife was given that visa. It's just a matter of getting in touch with them. This forum might not be able to give you more details than it has already provided you. It's up to you to take actions as soon and as much as possible.