Go to this site and get each version from 7 to 13 from here:
http://ootpdevfiles.com/ootp/
Then get every game type from version 14 to 25 here:
https://www.ootpdevelopments.com/ootp-prior-version/
Version 26 is still here on a sticky:
https://forums.ootpdevelopments.com/...lay.php?f=4070
You are not going to be able to activate your game. eSellerate is dead and gone. If it is active, great, you can keep playing but no one is going to activate it on the other side.
You want to install version 7. See if there is an import game option on the Main Screen (should not need to activate it) and then import the save to version 7. Then install version 8 and repeat. Walk it up al lthe way to version 26 using this process of importing from the main screen without actually playing it (and thus needing a license). When you get to 26 you should have the game walked up to the current version. To play it, you will need a license for OOTP26 but it's the end of the develoment cycle so it is probably cheap.