I have the same problem. I use IB to trade the products on exchanges I don't subscribe to( With most FCM you need to have real time datas to trade a product ). I recently subscribed to ICE Canada because I was losing too much on Canola trading blindly, even if I barely trade it 10-20 times a year. You should try to check the last native print ( delayed )on websites like barchart. With the last level traded, you get a better idea of where the native spread is...
Generally speaking - this isn't broker - it's the tech. CQG and Rithmic have a wide range of supported exchange spreads - but most retail platforms don't show them. I'd put IBs platform in the same position if you can't find them and support confirms they aren't there. Most are extremely illiquid though.