Unfortunately there's no easy way to get drivers for your printers, unless most of your printers can just use the manufacturer's universal drivers, in which case you'd only need to download a few drivers. Either way, the drivers themselves will need to be downloaded from the manufacturer's website.
Once you have the drivers, you will need to manually upload them into the Printer Installer database and specify which driver to use for each printer. Uploads can be done in the Administrator by going to Tools -> Driver / Profile Repository and clicking Upload. The specification part can be done manually, or in bulk via CSV file. To do the CSV file bulk selection, first export the list of your current printers by going to Tools -> Import / Export -> Data Manager and selecting Export and TCP/IP printers. Then modify that CSV file with the names of the appropriate 64-bit drivers, then upload the modified CSV file by selecting Update and TCP/IP printers in the Data Manager.