I checked Petfinder and that offers regular pet insurance. Our shelter will take any pet that gets sick back and treat it until it is well and then return it to the new owner. I know they give medications and and vet care if anything goes wrong soon after the adoption. Maybe you just ask your local shelter if they will do that.

Or...you could come get one of my porch kitties!!
(I hope you know I'm just teasing you!)