Is there a tag for comics that are more than 1 page

No. There is the comic tag for comics in general, which can be 1 or more pages. You can also use the isparent:true, ischild:true, or inpool:true meta search tags to check if the comic page is linked with another post, usually indicating multiple pages. Most comics are multiple pages though, so there's not usually a need to narrow the search like that.