Your fill plug is still good as is. You can make it nicer by removing the sensor and installing a recessed hex plug. If you want a new fill plug it is best to go to a Pantera vendor.
Here is an example hex plug for $4 that could fill the hole where the sensor is. I am not sure about the size you need but here is 3/8". You might need smaller. If you go this route be sure to put sealant on the plug threads.