I have found this from China on EBAY.
http://www.ebay.co.uk/itm/1315852528...%3AMEBIDX%3AIT
This is an ultra low noise regulated power supply according to them it is superior to normal LM 317 LT1086 and so on that sound hifi and Kabusa uses and many DIY use.
They make whatever voltage you need,in this case for the SL-1200 21-22V the technics can run on 18-25V so there is no problem with 24 V as well but to be safe just say you want 21V.
It connects just like any ather outboard power supply from OK suppliers.21V+ ti J3 and minus to ground post on motherboard.
Run it to the on off switch so you can turn it on and off woth the regular on off switch.
I have nothing to do with this firm i just wated to give you a very good product works perfect.
80£ free shipping in good looking box and perfect power,normally it goes through the customs whe shipped free at least in sweden.