I was told abput a way to get infinite monkey bombs on der reise. This works for the hardened maps and possibly in WaW but has not been confirmed. These are the steps. If you dont have the Classic maps, look in some of the Black Ops forums and your able to get them for free here I think.
1. Get monkey bombs from the Mystery Box. May take a couple tries

2. Use all of the monkey bombs

3. Get into a good room like the one right next to the teleporter with the grenades and MP40 next to it.

4. Buy grenades or you can use ones you have.

5. Throw a grenade on the ground

6. Pick it up using LB not RB like you usually would

7. You will pick up a monkey bomb rather than a grenade!

8. Once you run out of grenades, buy them for 250 off the wall. All four monkey bombs you get from the grenades pay for this many times over so youll be fine

9. Watch out for the grenade as it will still be on the floor. As long as you dont accidentally pick it up it will not kill you usually.

+rep and thank if this helped