You should look into getting a MatchsaverZ to mount to the pump
https://www.youtube.com/watch?v=vL9E7pu79Fc
I'm trying to find a 2-shot shell carrier like the one in the below picture. Want to put it on my 870.
"3gungear.com" is the obvious answer, but I'm not certain if they ship to Canada.
I think it would interfere with both the forend and if behind the ejector port the elastic loops will cover the loading port.
You could just get a Velcro card like S&J sell and cut it down to 2 and mount it sideways behind the port .