There is no magical place that has a stockpile of vintage parts from a company that no longer exists.
All you can do is ask around online or check Ebay to see if anyone has parts that you're interested in.
Keep in mind, the BA-F1 has very unique power output transistors, which are also used in the AU-919 integrated amp, thus if you were looking for the transistors,
they can be found in the 919 as well.
Also be aware of the 'black flag' caps which should be removed from these models as they are known to cause problems, so hopefully that was done by whoever did the "freshening up" you mentioned.
If you really were in need of spare parts, it would probably just be easier to buy another BA-F1 and keep it as a backup, or if another one happens to be in better condition or had more restoration, then maybe use that one instead, and keep the one you're using now as the backup unit.
