Nice tank. Fish look happy in there with all that cover, I had those same plants in an old tank of mine that i really liked, but then, they met some algae and turned brown and black on me haha.
I think they are plastic, not silk, but either way, I got mine from Michaels craft store for about $9 a piece. Michaels has a lot of plastic plants that look pretty good in aquariums..
that is an 80 gallon tank lol and the plant i got from tfp and it was a huge plastic pond plant being a cheapo like i am i bought 1 of them on sale with a discount coupon for 6 dollars, broke it all apart ant tied it to rocks with fishing line