You can get old versions of HPLIP here: https://sourceforge.net/projects/hplip/files/hplip/
One last thing... I notice you NEVER refer to the Printer app in Linux Mint, while I have mentioned it several times. I just want to make sure you are checking that app too, and especially regarding the wireless configuration. I'm pretty sure it will be required for wireless setup.
At present, no idea on Mint 18.3. They may have a schedule posted, but I haven't looked.
One last thing... I notice you NEVER refer to the Printer app in Linux Mint, while I have mentioned it several times. I just want to make sure you are checking that app too, and especially regarding the wireless configuration. I'm pretty sure it will be required for wireless setup.
At present, no idea on Mint 18.3. They may have a schedule posted, but I haven't looked.