You can find one hidden in secret rooms, behind doors that require keycards, or a Bullet Shop


You start off with 3, but you can find more through Bullet Shops or hidden around the level


You know where to find these. They're not hard to miss.

The Toolbox is an item that turns regular bombs into Homingbombs. All you have to do while having this item in your item slot is to press space. It will drop one Homingbomb onto the ground, subtracting said bomb from your regular bombs.

This part's easy. Put the Toolbox in the Bank's storage. Every time you want some Homingbombs, just...

1. Find Bank
   
2. Withdraw the Toolbox from storage
   
3. Make as many Homingbombs as you can carry(lvl1 carry lets you only carry 3)
   
4. Put the Toolbox back in the Bank
   
5. Collect your freshly baked Homingbombs
   
6. ???
   
7. Profit!

When you run out of bombs, just find a Bullet Shop and buy the regular bombs for 10 coins each. You'll save 20 coins everytime!(Homingbombs cost 30)