If you want OpenBSD to develop updates to match your particular NIC, you can wait and hope, contact the developer(s) directly, or do the development work yourself. Assuming you need a developer:
To the best of my recollection, reyk@ is the developer who has done recent work on a variety of newer Atheros chipsets. As I see it, you could
- Contact him to see if he is still working on Atheros updates.
- If so, you could ask if he already has a NIC with an AR5424 chipset available.
- If not, you could offer to send him your NIC (or laptop, if it's built-in), or buy him one.
Your other choices are to acquire a supported NIC or switch to an OS that supports your NIC.