I have an old Northgate OmniKey Ultra keyboard which is designed to work on PCs as well as Amigas. However, it has a few toggle switches on the back that need to be changed for Amiga vs. PC, so most likely that means there are some signal differences even though the connector is the same. You probably can't just hook it up and install a driver to make it work. You might want to check the Amiga Hardware Bible website to see if any connector devices exist then look for one of those. If you do get it working, many special PC keys probably won't work.
If you can find a Northgate, you can use them without extra hardware and there is software on AmiNet to let you use keys like PgUp and PgDown on Northgates. Id bet Northgates are easy to find on ebay.