I'm not sure what's available if you want gorillas only, but there are a variety of "ape," "great ape," and "ape-men" available in 15mm or roughly 15mm size.
Try Old Glory Blue Moon 15mm Deep Dark Africa "Jungle Man, Jungle Woman and their Great Apes" set for some oversized, or "great" apes. They don't look all that good in the photos, but minis sometimes paint up better than they look "raw."
Khurasan Miniatures also has some 15mm ape-men in its 15mm Fantasy Range that might do for gorillas.
Rebel Miniatures has some 15mm Monkey Boys that might do for you.
Irregular Miniatures has a 6mm Capture King Kong game set in its Tusk Range. No photo of the figure is shown so I can't guess at size, but the King Kong figure might work for you.
Finally, Safari Ltd. sells a line of children's toys under the general name of Toobs Miniature Figurines. The Toob's line has at least two sets with apes of some sort in them; the Wild Animals Toob and the Monkeys and Apes Toob. The Toobs sets are generally available at Michaels and other craft type stores, so you can probably find them. They cost about $15 USD per set, or "Toob," and that might be a bit steep for one ape in each set. And the Toob figures are "box scale," that is they are not sculpted to any constant scale, but are sized to fit the box, or toob, so the size might not work for you. From the photos and my experience with Toob figures I'd guess the size might be close enough to 15mm to work, for me at least, but I haven't seen the ape figures in person and anyway YMMV.
Oh, one last thing. Several times in the past decade or so various posters on TMP have started threads on 15mm Tarzan or animal fantasy armies. So you might do a search here for 15mm apes or 15mm gorillas, or 15mm Tarzan, and see what you get.
gets his hands on some fields and fences.
