So what you need now is the keyboard to FPGA interface ya? Hmm... I've never done this before, but upon googling around, I now understand why you need UART.
Unfortunately, I dont think I could help you any further. I have no idea on implementing UART on an FPGA. I suppose you will need to make your own UART code / bit-banging. But considering the fact that UART are very widely used, I'm sure there are pre-built modules for it, either by the FPGA developer or somewhere on the net.
If you ever think of using a PIC instead, then I should be of more help