The IC might be an ordinary one that has a "special" number so that replacements can only be bought from the company making the product they are used in. Then they can charge a very high price for the replacement part.
Maybe the IC is a custom one that nobody else uses. Then again they can charge a very high price for a replacement.
Yeah, like some old video RAM from a early 80's video card with 4Mb RAM etc? In late 80's they went to those long DIL chips with 22 pins or something.
If there's a matching set of 8 or 12 ICs in your junkbox they could be old RAM chips that you pulled from the sockets (in the good old days they put chips in sockets in PCs, before everything became "throw away").