You can indeed respace an 8 spd cassette to work with 9spd Ergos, had to do that myself having bought a complete bike where someone had used all 8spd apart from the Ergos and it obviously didn't index correctly. I had a junk 9spd cassette with loose spacers, swapped them for the 8spd spacers and set the limit screws so you never reach the 9th 'click' - works perfectly. That said Andyp's offer sounds like a good option! You can't fit 9spd cassette on 8spd freehub.
You can indeed respace an 8 spd cassette to work with 9spd Ergos, had to do that myself having bought a complete bike where someone had used all 8spd apart from the Ergos and it obviously didn't index correctly. I had a junk 9spd cassette with loose spacers, swapped them for the 8spd spacers and set the limit screws so you never reach the 9th 'click' - works perfectly. That said Andyp's offer sounds like a good option! You can't fit 9spd cassette on 8spd freehub.