Just FYI I found some replacement corners like these on amazon. They’re not available anymore but I have some left if you want to pay shipping to have some backups.
Yescom 10pcs Replacement 3 Way Nylon Connectors Corners for Grow Tent w/ 16mm 5/8" Resistance Poles https://www.amazon.com/dp/B00EJQWX4C/ref=cm_sw_r_cp_api_i_nIMLDbG1GCB73
Would these work ? Yescom 10pcs Replacement 3 Way Nylon Connectors Corners for Grow Tent w/ 16mm 5/8" Resistance Poles https://www.amazon.ca/dp/B00EJQWX4C/ref=cm_sw_r_cp_api_fabc_eOm8FbJEKBXRT?_encoding=UTF8&psc=1