Finishline sells them with the oil pump. I have not had a problem. https://www.finishlinemotorsports.com/big-block-buick-loaded-front-cover.html
I have a ProForm cover on my engine and it works fine however I did not buy it it was on the car when I got it so I could not tell you where to buy them offhand.
Which ever cover you end up getting make sure to use a booster plate, adjustable pressure regulator and a shim kit to get the proper end clearance on the pump gears.