While the TC will be the best to answer this question, I thought I could share some information as I myself have tried to look for the right materials (with proper friction and all).
I could not locate the one i purchased in the past. Just some ideas here: https://www.rugstreet.com/PROD/artificial-turf-by-the-square-foot.html. TC, please advice.
I concur with Elizabeth on deferring to the TC for official guidance
However, there is a great guide to field construction midway through the team resources page at http://robocupjunior.squarespace.com/team-resources-1-1/ that provides part sourcing information which could be helpful
Thank you, Chris.
TC, green mat is no longer available from Lowes (as the link indicated in the guide). Someone emailed me to request exactly that; and i think it will be better if it comes with the blessing from TC . 
I have searched high and low for some materials may match up with it. If you think the materials from the link I provided is not appropriate, please advise.