I'm with Dfrost on this. That is likely a 11 /23 or 12/23. The simplest thing to do is drop the smallest sprocket and add a 26 to the other side of the cassette.
That is assuming you don't need the smallest sprocket.
And you have the tools or a shop willing to do it for you and access to a spare sprocket.
And it is possible to clock the cog yourself by filing of the long tab on it and rotating it to the correct position. It only needs to be clocked to the adjacent one.
And you may not even have to adjust the cable tension or limit screws for it to work.
Obviously you have to check that's true.
And it is difficult to find a new cassette that actually suits your needs rather than the population as a whole.
Pardon me, i just realised who the o.p. is. He will be able to figure it out.