Eh, if you continue the Overtime mode from your 72hr game (not selecting from menu), you should still have all your previous stuff in your inventory (chainsaws and such).

Even without the mini chainsaws, its not too hard to kill the special forces people. Just get an weapon that's just as good, like the Katana or Battle Axe.
I still prefer disembowelling them though.

But generally, the best way to get by them is like how you treat the zombies: By avoiding them. Running up to them from far will just reward you with a face full of bullets.

And on how to collect the items: Start from the shopping mall, then work your way counter-clockwise through the mall. Make sure you grab lots of wine from the mall beforehand though. Getting stuck in the middle with no healing items: o noes

You also need to collect 10 queens after all the items as well. Aha. Still not too hard though. Give it another try.