"Command Not Found" errors typically mean you're not in the right directory. if you type dir in a command prompt you should see the file(s) you're referencing.
You have two options.
Change directory to wherever your command files are:
Code:
cd \androidsdk\platform-tools
fastboot flash recovery <path to>\recovery.img
OR
Reference everything by path
Code:
c:\androidsdk\platform-tools\fastboot.exe flash recovery <path to>\recovery.img
In either case, change <path to>\recovery.img to where your amon ra img file is.