Saw this today, AY-3-1015 UARTS at ROCKBY ELECTRONICS
If you want a real hardware UART for A$3, take a look halfway down Page 3 of this clearance sale.
Those are good chips and were popular in years back. About your source I know nothing.
Here in the UK i've used Silicon Ark for lots of old TTL chips as well as M68K devices, LEDs, IC sockets etc. I've found them cheaper than ebay.
I think that I used such a beast in my first floppy disk controller. It must have been a special ceramic case edition with a clock frequency up to 4 MHz what made it usable for read/write FM data speed. Higher speed was not achievable with my 6809(?) microprocessor.
I recall some devices with them, back in the 1980's. Do you forget that you also need a clock chip to supply the timing to the UART?
Bet they are pulls from old equipment with no testing done.
Sounds like you used a WD FD1771, popular before the uPD765 from originally from NEC.
That was the next step after my UART approach. Killed several controllers because the 5V and 12V did not always come up in the right order. AFAIR the FD1772 had a single 5V supply only.
hehe - a long time ago, first Z80s etc.