mortise with pentagon hub

Trying to find a mortise for my Larson storm door. I ordered a new quickfit latch set that was supposed to fit with no issue and it would have, however, the original mortise has a square hub, the new latch is set up for a pentagon (5 sides). I am having trouble finding a replacement to work for one or the other. I want a new black latch to match all my other accessories, but can't find one with a square piece. Also can't find a new mortise with a 5 sided hub to match the new latch, any help would be appreciated.