Can't find custom block php code in the database
Universal solution to find something you know is in the database is:


Dump the entire database to SQL file.


No compression, or uncompress after downloading.
Use one row - one line format - disable "insert many rows in one INSERT statement" and similar options.
Also, disable anything that looks like "save BLOB columns in hex format" - you want serialised variables in human-readable form.

Use grep or similar text search tool to search for the string parts you think characteristic enough to the row you need to find.