Uncle Mike's uses a sort of neoprene material on the outside, and something slick on the inside so that the gun draws cleanly. They're better for small guns though.
There's a material called corfam that, if used in a thick sheet, is supposedly similar to leather in construction, so that might be an option if you want to make it yourself. It's unlikely you'll find many leather alternative holsters, as the demand really isn't there...the majority of CWP holders aren't also PETA members. I don't have any problem with vegetarianism (I'm almost there myself - but for health reasons), but that's just how the demographic breaks down.
One option - and I mean this in a totally constructive way - is to check with a group of folks that would be more likely to be pro-animal vegetarians while also carrying firearms. They may already have a solution worked out for this problem. The only group I can think of that would fall into this category would be Pink Pistols (check Wikipedia if you don't know what they are). They probably have a forum with at least one thread devoted to leather alternatives for holsters.
Just tell you wife in advance why you're going to that website. :laugh: