The original Bitcoin Core client can bulk import from a text file, if that text file is actually a batch file with RPC commands:
"C:\Program Files\Bitcoin\daemon\bitcoin-cli.exe" importprivkey L4mP3joYEhSv1ofdsWbz8xEmqCmYK9vGyi8mJmWWbh79Xx2NsS1M importedaddress1 false
"C:\Program Files\Bitcoin\daemon\bitcoin-cli.exe" importprivkey Ky2EGjWLhfKv1sWnPcuN4SHF2iALj6SfK7hoLWKx5T4zMqXg7aT9 importedaddress2 false
"C:\Program Files\Bitcoin\daemon\bitcoin-cli.exe" importprivkey KzrZ4DULdVWFqpF48pdJicFJfX5dqrhxBkqDnT4HRkCswdFy3Eo4 importedaddress3 false
"C:\Program Files\Bitcoin\daemon\bitcoin-cli.exe" importprivkey L2ELWXewr1PQnMwFDpfobHFqspyM6g1noM4uzkCMgoSZTSf3sQJF importedaddress4 true
With some text editing you can make your list of privkeys into such a list of commands, and save it as import.cmd and run (notice the last line has "true" at the end to start reindexing).