Yes you can buy endophyte free fescue but...it is much more difficult to establish and will not stand up to abuse as will the infected variety. The endophyte helps the fescue maintain its vigor, resistance to insects, low moisture and overgrazing. There is a new fescue on the market that while still containing beneficial endophytes, does not contain the ones responsable for problems in wildlife and livestock. I don't remember the company but a search on the net would probable show it. You are right that most animals, including rabbits deer, horses, cattle etc. , have some problems when only fed infected fescue. Low conception rates, rough coat and general unthriftiness are some of the usual symptoms. Overseeding with a legume such as clover seems to dilute the endophyte's bad issues. Your best bet may be to spray at least 2 times 4 weeks apart with roundup per the label then overseed your intended product in accordance with the products labeling.
Sorry for the long post.
Hope this helps
Greg H