Since this achievement is so hard to get and there is very little information about this game I'll try to help you guys out as best i can.

There is 162 weapons, all you need to do is pick them up for it to register as you have collected it, you also must finish the chapter so you get the results screen at the end, quitting out or going back to town will make the weapons you picked up not count.

You should defiantly go for this achievement last or after you have completed the story mode at least twice AND done the Treasure Hunter achievement, reason for that is because at this point you will have most the weapons done already. When you do the Treasure Hunter achievement make sure you pick up every weapon that it drops. Also when it come's to wishing wells make sure you donate TWICE, sometimes three times because some wells drop different stuff on the first and second try and some even on the third.

Slice Weapons : 48
Blunt Weapons : 96
Guns : 5
Bows : 5
Potions : 5
Wands : 5

Now these are the weapons most commonly missed by people.

Chapter 3 - Scimitar Shark - Twig of Destiny

At the very beginning of the chapter go to the left of the raft. There are three chests. First a money chest. Then a chest in plain sight next to the lighthouse (in here is the Shark Scimitar). Then to the right of that one, behind a tree and against the lighthouse is another chest (Twig of Destiny).

Chapter 3 - Wizard Staff

Once you leave the town, and see two chests, you walk past a well that you can't wish at and the house following it has it (Wizard Staff) leaning against the rocking chair.

Chapter 6 - Spoon of Destruction

For the Spoon of Destruction, the only place that I have found it was in the boiler room level by the second wishing well on the level. After you fight off the rats surrounding it, sink money into it. Every time I have used it, the well shoots out only spatulas and Spoons of Destruction

Chapter 10 - Flamingo Trumpet

When you start the level, simply go to the bottom right box. It can sometimes be hard to see. Hit it open and there it is.

Chapter 10 - Invisible Sword (Plus achievement HOOOO!)

When you get to the water area with all the bear traps you can walk through the waterfall. Sometimes it can be sticky and hard to work your way back so keep wiggling and you should get it.
Once you get in the back area it changes view and shows you a chest. I couldn't get to the area but when I accidentally went back out and died on a bear trap it automatically dropped me off at the chest.
Once you bash it open inside is the weapon. Then go to the doors and it transports you back to the other side of the croc grabbers.

Chapter 10 - Water Pump & Water Bellow

This one is a little tough. After passing the Croc Grabbers, you can jump up on top of the croc head. However be careful this is very dangerous, on top of that you can even die when on top of it by being thrown into the wall to harsh. Once on top jump to the right and open the chest and both are there.

Chapter 11 - Rainbow Sword

This sword is on the beanstalk level, right before you fight the first cloud men. Before you walk through the doors there is a cloud off to the right floating on it's own. Jump to it and on it is the rainbow sword.

Chapter 12 - Excalibur

After the three level section where the yellow balls roll down trying to hit you, you will pass a wishing well. Drop down to the next area. In this area nothing will happen, but right on the next ledge there is a bell to ring. Be careful not to fall. After you ring the bell a compartment in the area you just were will open. Jump back up to it and after you fight gnomes for a bit go inside the alcove to get the Excalibur.

Chapter 14 - Blacksmith Sword

The sword is directly in front of the chessboard in the Chapter 14. It stuck in the candle next to the beer cup on the left side. To get to the candle, climb onto the fruit on the left near the pitchfork and then jump onto the plate. Then walk along the edge to the cup. Be careful when you jump and walk around the edge of the cup if you fall in you die. Then when on the other side of the cup jump up to reach the sword.