Any options outside of the silicone molds?

You can use the plastic molds. I made some last month using the candy melts and plastic molds. If you want to make them out of fondant, go to you tube and do a search for how to make fondant seashells. If seems I saw it there somewhere! lol

I bought an inexpensive Wilton shell mold and used white chocolate chips. I dusted with Wilton pearl dust or whatever its called. Very easy and they looked nice. I have a flipflop cake with the shells in my pictures.

I used a Wilton Shell Mold that I bought at Micheals and put fondant/tylose mix in it. Put it in the freezer for a few min and popped them out. Let them harden for a few days before putting them on my beach cake. Hope that helps!

Candy molds work, and I think there is a shell soap mold.

If you want the more realistic looking shells, you'll have to go with the silicone molds though.

I use Wilton molds, other molds found online and "soap" molds that are made of the same thing. I don't use chocolate because, well to me, some end up looking like shiny soaps. I use thinly rolled fondant. They end up looking and feeling just like real shells.

Then I dust or paint or both with a variety of colors of dusts.

I CAN'T GET THE PIC TO ATTACH!!! I AM GOING OUT OF MY MIND!!

So here are the links...

http://cakecentral.com/gallery/1212289

http://cakecentral.com/gallery/1212289

http://cakecentral.com/gallery/1484079