Hi @carloslwalde
The [https://www.groundhoginc.com/PDFs/HD99%20Hydraulic-(Parts).pdf|parts list] shows that part #57 is part number [https://www.groundhoginc.com/part_detail.php?iPartID=205&iProductID=8|H640] which is seems can be ordered from Groundhog.
Alternatively, search online for [https://www.google.com/search?client=firefox-b-d&q=groundhog+H640|Groundhog H640] to find suppliers that suit you best. (supplier examples only)