I'm currently looking for a single player RDR game save which has unlimited max ammo/money, but not %100 complete. Or if there's a tool too edit the ammo and money from your own save, that will do fine.
Try this http://www.xpgamesaves.com/files/file/2239-ccaveman84s-red-dead-redemption-single-player-mod-save/ Found using the Search Button!