I found a Tandy 1000 EX complete system on Craigslist. It was destined for the scrapheap because it didn't work. In this video I troubleshoot the machine and give you a tour of this pretty cool 80s computer.
I found the replacement chip from Autogard UK:
http://www.autogarduk.com/
They may be the last source around for replacement Tandy and many other old and obsolete components. They were a pleasure to deal with and I highly recommend them.
(I was not paid or compensated in any way to endorse Autogard.)