Hobby Lobby has buttons that are in different shapes, you can also try Etsy.com for mosaic supplies

Try these:

http://www.marylandmosaics.com/

http://www.monstermosaics.com/Porcelain-and-Ceramic-s/167.htm

I got some fun stuff on ebay some years ago. I check back every now and then. Here is a link to whats there now - its gotten more expensive and less useful to me but I look just in case.
http://www.ebay.com/sch/Glass-Mosaics-/163778/i.html?_from=R40&_nkw=handmade+ceramic+clay&rt=nc

I think the person I bought some stuff form a few years ago might have moved to Etsy. Below is a link to some stuff there. Again some of it seems over priced to me. Good luck.
Kathy

Here is a link that might be useful: Ceramic shapes on etsy

I kind of like these hearts. But it doesn't say how many on average.

I would love to make my own. Don't have the time or a connection to a kiln right now.
Kathy

Here is a link that might be useful: Heart shapes for sale

Also think Beads. Hobby Lobby has a huge assortment of glass beads, many many fun shapes and colors from animals to flowers to whatever.

http://www.mosaicartsupply.com/index.aspx

http://www.mosaicsbymaria.com/

http://www.muranomillefiori.com/

http://stores.happycraftnsmosaicsupplies.com/

http://mosaicsupply.com/categories/Glass-Mosaic-Tile/

http://www.mosaicrocks.com/shop/category.asp?catid=31

Thanks all! I'm going to try Hobby Lobby again (I love beads, I just don't like the annoying bead holes). And I've seen lots of good things I'm going to buy at these sites you recommended, I just don't like the prices! Thank God this is just a hobby for me because I don't know how real artists make it at these prices! :)

We have a gem store near us that also has beads and stones. Some of the glass items are quite inexpensive to a strand.
Kathy

I look for beads that will lay flat with the holes running vertically so they dont show. sometimes the holes add interest. and hobby lobby does half price sales on their beads about twice a month which makes them affordable.
There are a couple shops on etsy that sell awesome cermaic tess-
https://www.etsy.com/shop/TinkerTiles
https://www.etsy.com/shop/BarbsCottage
https://www.etsy.com/shop/mosaicmonkey?ref=shop_sugg

I dont know these people, I just like their things. also buttons can make fascinating and beautiful tess and many people sell them by lot. I love to sort buttons.

I like to mosaic with the rims of saucers. That's an inexpensive way to go. Buy a saucer or plate at a garage sale or thrift shop for 99 cents and get 25 or more pieces of tess. It's more finicky to work with because the thickness is not uniform, but I love the amazing variety of color and design.

Here is a link that might be useful: Silva's blog

In my area you can usually get saucers for a quarter or so, and usually nice ones that are easier to cut than plates. I have a thing for saucers too.