Another option besides RR scenery is Wargame scenery.
Here are a few links that might help.
http://www.librarium-online.com/forums/scenery/88129-my-friend-needs-your-help-creating-jungle-scenery.html
http://jonswargamesminis.blogspot.com/2011/03/cheap-jungle-terrain-2.html
http://www.matakishi.com/jungle.htm
http://15mmvsf.bagofmice.com/Models/terrain/terrain_how_to.htm
http://www.games-workshop.com/gws/content/article.jsp?categoryId=cat440312a&pIndex=1&aId=3800025a&multiPageMode=true&start=2&_requestid=1146007
As you see, a lot of these use aquarium products like you have already done but make sure you check out dollar stores, etc for deals.
Games Workshop makes plastic plants but they do get expensive and would most any bought scenery set.
There are also other products out there for different scales that could work. 35th scale ferns for example would probably still look ok especially if in the thicker part of the jungle, and anything labeled small in 35th should be big in 72nd.
Hope that helps, looking forward to seeing what you come up with (and, by the way, what Marines did you use in your beach landing diorama?