New or second hand, Paul, for the A23? If it's the latter, then the best plan is to start a wanted ad in the classifieds or look on ebay (for both). If you're looking for a new A23, then talk to Simon at Hi-Fi Sound:
https://www.hifisound.co.uk/
That's where I got mine from, when I had it (he does them to order only) and he's a great guy to deal with.
Other than that, as I have a lot of experience with all versions of the 103, including the Pro, I can say from experience that it works really well with a Highphonic HP-T5:
https://www.ebay.co.uk/itm/Highphoni...-/264564360652 as they were designed to work together, due to the fact that Highphonic make the Pro (or rather modify stock 103s to their spec), so that would be a great match, in terms of synergy.
Hope that helps:cool:
Marco.