You might want to check out Amazon.com or any other store that sells EV3 alone.

http://www.amazon.com/LEGO-6029291-Mindstorms-EV3-31313/dp/B00CWER3XY

Please note that its contents may be slightly different from the LEGO Education EV3 packaging but should be good for your second Robot. Read the below description on its contents to see if the contents will meet you needs. Mostly you will need to worry about the sensors but it could also be others things such as wheels/tires depending on your design.

 
Best Regards,
Vinayak

Date: Sat, 2 Aug 2014 10:50:04 -0400
From: [log in to unmask]
Subject: [VADCFLL-L] Purchasing more than 1 robot kit for an FLL team
To: [log in to unmask]

Hello,

My name is Sarah Jaka and I am the coach for Team #1804 in Chantilly, Virginia.  I was checking out the Lego Education Store to purchase two robots for my team.  I was only allowed the option to purchase one kit since I only have one team.  How can I purchase two robot kits? 

Thank you,
Sarah Jaka
To UNSUBSCRIBE or CHANGE your settings, please visit https://listserv.jmu.edu/archives/vadcfll-l.html and select "Join or leave the list".
VADCFLL administrative announcements are sent via VADCFLL-ANNOUNCEMENTS-L. Visit https://listserv.jmu.edu/archives/vadcfll-announcements-l.html to subscribe.
To UNSUBSCRIBE or CHANGE your settings, please visit https://listserv.jmu.edu/archives/vadcfll-l.html and select "Join or leave the list".
VADCFLL administrative announcements are sent via VADCFLL-ANNOUNCEMENTS-L. Visit https://listserv.jmu.edu/archives/vadcfll-announcements-l.html to subscribe.