Please do not look at this answer as being sarcastic.
Have you looked at using a PIC or Motorola Nitron for this task?
Having seen the cost of UARTS for this, and they still need a micro anyway, might be best option as both companies supply a protocol stack for this anyway for free
Or you could use a Startech (Exar) UART like the ST16Cxx as they have 2 serial channels that can do 8/9 bit and clocked independent to each other, with or without FIFO