where can i find old firmware downloads for some old Zyxel Switches

I am clearing out a load of old network switches and zyxel kit, I don't just want to bin kit - (not very green) and these are perfectly good old switches, but before I give them away or sell, i'd like to upgrade to latest firmwares available. Problem is the good old ftp.zyxel site has gone now, and new site doesn't even recognise these old model numbers! Any help would be gratefully received. Thanks