The manuals for the Tandy 1000EX/SX, which I *think* use a chip that's functionally identical to the one in the TX but I wouldn't swear it's the same revision, list it as Tandy part number 8040684; it's an 84 pin gate array.
Some years ago there was some outfit in the UK that had NOS spares for a few Tandy 1000 proprietary chips (I remember seeing a Youtube video that called them out as a source for the timing chip in the 1000SX), but my recollection is that they disappeared/ran out/whatever. Seems really unlikely you'll be able to find one without scavenging it from another unit.
What makes you certain it's the big blue that's damaged? There are buffers between it and the RGB output so it'd take a little work to kill it, I'd try replacing those and the RAM first depending on the symptoms.