You might try Bob at Vintage Electronics. I got an Aiwa kit from him in the past. Also, Fred at marrscommunications.com may be able to help.
Sony bought out Aiwa a while back but I didn't have much luck trying to find parts for my machine. A lot of places listed the part but upon ordering it, I was always notified later that it was no longer available. One of my pet peeves really. If the part is NLA, take it off the website or list it as such!