There isn't a spacer ring which makes this unusable
As per my PM I've managed to find you a spacer in my spares box, (lucky I don't throw things away), and I'll pop it in the post tomorrow. It was not with it as my bike does not require the use of one, and it wasn't actually missed off, it wasn't actually advertised as having one as I'd forgotten all about it.
So for clarity, as the cassette was not advertised with a spacer, therefore the lack of one didn't make it 'unusable' as you say, it just meant that if I wasn't the amenable, hoarding kind of a guy I am you'd have had to source one, but any LBS worth it's salt should have loads of these from fittings that haven't required the use of the spacer.
FYI, for future reference, you could also have used your old as well.
If you ever lose one you can also
BUY them singularly tool, so don't let an LBS fool you into a buying a cassette if you do.
Glad to have been of service on this occasion, ride safe