I assume you mean Windows *Phone* 8.1? Well, there's obviously any that are sold by TMoUS MVNOs (check Wikipedia or something). There's the ATIV S SGH-T899M, which was an 8.0 launch device but still has decent specs and is fully compatible... you have to get it from Canada, though. Probably any other phones from the same carrier (TELUS Mobility) will also work. I don't know of any others that are going to be fully compatible but which they don't sell; there might be a few, though.
Do not private message me with questions that should have been posted on the forum! Not only are you wasting your time - I'm not going to bother writing an answer to such a question for only one person - but I will probably block you from PMing me in the future as well.
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