Yeah, the EU version of Call of Duty: Black Ops usually uses the BLES01031 title ID.
The RAP files for that version are a bit harder to find, but most people just grab them from NoPayStation / PSNStuff RAP packs instead of searching for a single file. Those packs usually include the BLES01031 RAPs along with the DLC PKGs.
Also make sure:
Your game ID matches BLES01031
The RAP file goes in /dev_hdd0/exdata/
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You activate it with PSNpatch or similar
If the RAP still doesn’t show up, another option is installing a DLC fix PKG, which some users say works without needing individual RAP files.