Microsoft Optical Wired 1113/Usb/Ps2 Compatible Black | 000300247426 | Cash Converters
Standard USB Optical Mouse - Black
PS/2 and Serial Wireless Mice for DOS Gaming - a few options, and quick reviews (in comments) : r/dosgaming
MICROSOFT Basic Optical Mouse PS2 /USB for Business 4YH-00007 - 1PC.co.il
Honglei HL-022 USB to PS2 Adapter,PS2 Keyboard and Mouse to USB Converter Cables, for Keyboard and Mouse, Plug-and-Play,No driver required,Black: Amazon.co.uk: Computers & Accessories