It's not on the UK market because CAA refuse to give it an approval. The reason is that the record function allows RT to be recorded and re-transmitted, something that not unreasonably they think is potentially rather dangerous.
Of-course, because the A23 is there on the US market, good second hand A22s are very cheap out there, and it's worth looking on places like US eBay for a bargain.
Same applies to the A4, which is an A23 without the VOR receiver.
G