I don’t have a tumbler, but I have made sea glass or beach glass with
a foredom hand tool. This is of course no good if you need quantity,
but it is fun to do because you can carve the shape of the glass. You
can also carve a design in the back of the glass and leave the front
clear. I made a bunch of hearts this way.
I think most beach glass is actually old coke bottles - the glass
used to be quite thick. I have purchased some mineral waters in cobalt
blue glass, which is a pretty color, but I would check out the exotic
drink section of a local grocery store to see what kinds of bottles
Also, if you need quanitity, how 'bout a recycler? Good luck, beach
glass is really fun and versatile and looks great with faceted stones.