What fiber optic network interface card do I need for a WAN connection
You don't want to buy a "fiber card". What you want is a card (or preferably a switch) that has either SFP or SFP+ ports.
This will allow you to purchase cheap optics depending on what you need, and will ensure that you're future-proof if you need to upgrade or change optics in the future.
As for what type of optics you'll need, that's a conversation you will need to have with your ISP. Whatever you have will need to match whatever is on the other end of your fiber pair.
You need to find out what standard your ISP is using before you can start shopping for hardware to connect to it.
IF it's a fiber ethernet variant then you can use a network card with a SFP/SFP+ slot (SFP is for 1 gigabit, SFP+ for 10 gigabit) and a suitable transciever module.
If it's GPON then internal interface cards for PCs don't seem to exist, it seems you have to buy a seperate "GPON modem".
If it is some legacy telco standard you will need different hardware again.