First ... IMHO a rimfire that is dedicated to solely hunting and not making tiny groups DOES NOT need or warrant a scope with an AO, esp for game the size of fox. 2-7x and bee happy.
BUT, if you feel the need for an AO's scope, Leupold has their 3-9x EFR AO, Nikon has a similar version as does Weaver ... there are plenty of choices. Out to 125-150 yards I cannot see the need for more than 9x for fox sized game (or squirrel for that matter) OTOH, I'm sure someone will disagree and tell you a 6.5-24x50 AO is needed. Good luck with that.
