I haven't had the chance to start on RE4 cheats yet, but if anybody else is interested in finding infinite ammo/item mod cheat its important to remember how RE4 stores values for items. Here is an older guide that should help understand how the values work.
https://steamcommunity.com/sharedfiles/filedetails/?id=233436010
In short all items are saved as an array of bytes that contains a bit of information on the item (quantity, upgrades, ammo, etc...) because of this you cannot run a 32 bit search for ammo. So a handgun would look something like this:
23 00 01 00 00 00 00 00 38 00 10 05 00 00
00 23 Handgun ID
00 01 you have 1 handgun (this would be the value for stackables as well so a box of ammo would have 1 bullet)
00 38 upgrade ID
00 10 you have 10 bullets in the handgun
05 00 00 is the location and orientation the item is in your inventory.
[Edit: oh before I forge to mention, unlike the other RE games the different grid based inventory system makes it trickier to just mod in whatever item you want. You MUST have room in the inventory for that item before you edit the item in or the game will crash because it doesn't know how to have to separate items in the same space. So make sure you know how large your item is and make sure it's in the right space/orientation before you put it in. ]
Hope this helps. If somebody hasn't found it in the next few days I might be able to get something a little more solid next week.