Hi Jan,
If you have access to IBM Passport Advantage, you can find the part numbers here:
https://www.ibm.com/support/pages/downloading-ibm-db2-version-115-linux-unix-and-windows

Keep in mind that once you install the HPU 6.5 GA, you will need to upgrade to the latest HPU 6.5 FP4 to make sure that HPU is able to unload data from the latest Db2 releases.
There is a HPU V6.5 FP4 IF2 (latest available at this moment), where you can install on top of HPU V6.5 FP4 to have the latest fixes.
Related to the license information, please refer to the following link:
https://www14.software.ibm.com/cgi-bin/weblap/lap.pl?la_formnum=&li_formnum=L-LHYN-BCD43Y&title=IBM%20Optim%20High%20Performance%20Unload%20for%20DB2%20for%20Linux,%20UNIX,%20and%20Windows%20V6.5%20trial%20Multilingual%20eAssembly
I hope that helps!
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Cintia Ogura
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