First, welcome to the forums! I hope you enjoy building computers as much as I do.
I cannot find any compatible motherboards
There are numerous motherboards that are compatible with your CPU. It needs to be an AMD motherboard and have socket AM3+. On newegg
there are 51 motherboards that have that socket. To confirm the motherboard will work with your CPU, select the motherboard and look at the specifications tab - it should say something like "CPU Type." Provided FX is one of the types listed, then you should be good to go.
If you're still not satisfied, find the manufacturer's website and search for the motherboard. You'll have to dig around (maybe check the manual) but you should be able to find a complete list of known compatible CPUs - just look for the 8320.
Hope this helps.