You can get them here, but these might be small: http://www.save-on-crafts.com/beachseashore.html I got mine last year at Homegoods. Some of the nautical decor websites also offer them. They're called glass floats, glass buoys, nautical glass buoys -- be sure to search using plenty of names to find them at the best price!

Here is the link where you can find glass floats

http://gonautical.com/floats-buoys-c-2_93.html