Automation of converting pdf to pdfa2b

I'm trying to figure out how to convert pdf's to pdfa2b format for archiving. The batch process only takes in 600-800 files at a time, and we have over half a million files. It would take an eternity if we do it one by one (probably 20 months at this rate). Any help is appreciated. Is there a way within Adobe to achieve automation or would anyone be able to help me pointing in right direction with respect to open source scripts. 

Note: Apart from adobe tools, Ive also tried using Ghostscript. I'm hitting a wall with respect to adding the proper color profiles. 

			Device process color used but no PDF/A OutputIntent
				Has Output Intent
				Base color space name
				Outside visible page area

    gs_command = [
        r"C:\Program Files\gs\gs9.55.0\bin\gswin64c.exe",  # Full path to the Ghostscript executable
        "-dPDFA=2",
        "-dBATCH",
        "-dNOPAUSE",
        "-sDEVICE=pdfwrite",
        f"-sColorConversionStrategy={color_conversion_strategy}",
        f"-sProcessColorModel={process_color_model}",
        f"-sOutputICCProfile={icc_profile_path}",  # Path to the ICC profile
        "-sPDFACompatibilityPolicy=1",
        f"-sOutputFile={output_pdf}",
        input_pdf
    ]