If I got the dates near accurate, in or around July of 2017, Deere stopped using the 260 for production and started using the 260B. The 260B is not only an updated version, but also requires a different sub-frame mounted to the tractor. When member USAFRet was looking into getting a 260 from the gentleman in Iowa that Sulley mentioned, the search for a sub-frame kit began for him. IIRC, Deere no longer had any but he came across another member here that was selling one. I believe he got lucky and probably found one of the last ones available in the country.
There also was another thread recently where the asking member has a newer 1025 (MY 2018 I believe) , and was curious if anyone knew if the sub-frame for the 260 would actually fit. He was looking at getting the 260 and sub-frame in exchange for labor. IIRC, he mentioned his dealer would swap the sub-frame from the older tractor to his for $500. I don't know if he went through with the deal or the actual outcome.
My point is, if you're looking at one of those 260s from Iowa, if any are still available, you'll need the sub-frame for the older 1025s, and you'll have to verify it will work on a 2019 1025. I think it will, but no guarantee, as I haven't yet heard anything definite. Finding the sub-frame for the 260 is going to be the real challenge in the first place. You may end up with no other choice but to go with the 260B and its sub-frame.
You'll also need the power beyond kit if your tractor doesn't already have it.
If you're handy and mechanically inclined, consider installing it yourself. From what I understand, installing the sub-frame is pretty easy.