There's a Sony 5.5" CRT on eBay now, don't know if it's correct for your set or not.
http://www.ebay.com/itm/Vintage-Sony...item4d02a9ab4a
And a 9"
http://www.ebay.com/itm/SONY-9-CRT-U...item2c51fcb951
Whoops, I see you said it's about 7", well I'll keep looking.