IRIG time code is pretty old and unfamiliar to most engineers, so I'm guessing that you won't find any ready-to-use FPGA code.
There are several IRIG-B formats. Which one do you need? B122 is fairly common.
You may get better assistance by asking smaller questions, such as how to demodulate the AM sinewave, or how to assemble the serial bitstream into data words. Be sure to provide enough info for the average reader to understand what you are talking about, and be sure to explain how the IRIG signal gets into your FPGA.