If the hardware item is not supported by the underlying version of FreeBSD, then it will not work with m0n0wall as built.
Potential workarounds are:
1) Find the source code for the driver, compile it against the applicable version of FreeBSD, and then modify the m0n0wall image to use the compiled driver. This is generally thought to be beyond the reach of most m0n0wall users.
2) Try a development version of m0n0wall 1.8. It is based on a more recent version of FreeBSD and may support the card.
3) See if a recent version of pfsense supports the card. It's not m0n0wall, has higher hardware requirements, and is more complex. But if the card is supported, perhaps you can live with the rest that comes with it.
4) Forgo using an unsupported card and use an external, networked AP. I don't think you can find one that will not work