Hi DaveS
Scanners configured for the Seaward Europa / Supernova should work with the Kewtech KT77 off the shelf.
Im sure I saw some sellers on a well known auction site selling preconfigured cheap scanners or you could, if you can deal with the hassle, make up one your self.
Most EPOS scanners that have a RS232 cable option such as the Datalogic Touch series, or Zebex z-3220 will work with your tester.
If you decide to go through the hassle of making one up, there are a couple of issues.
First is that the rs232 (serial) plug will have to be removed and a new one soldered on with the correct wiring (and gender). Pat testers usually supply the voltage to power the scanner through the pins of the RS232 plug. This can be a bit of a pain as the colour coding of the rs232 cable from scanners varies by manufacturer. I have usually continuity tested the existing lead before chopping the end off to work it out.
Second issue you will have is the scanner will often need reprogramming to set the correct baud rate, data bits, stop bits and parity that you particular tester uses. This can be done using configuration barcodes supplied with the manual of the scanner.