The the way I "harvest" safety glass
I go on a regular basis to my nearest recycle center to look for safety glass. The best stuff is a double glass safety glass balcony door. That way you have lots of the same colored glass incase you are making a big piece or a series of work and want to have the same color in all the glass. I stay away from glass that has green or lots of mineral build up between the glass.
I will take the glass home or if that is not possible either way do the following.
Clean it with Ajax or just plain soap and water and scrape it with a razor blade to get any stuck dirt off it. Make sure also the frame is clean for things will fall off it into your glass for sure.
Place a tarp under it.
Tie it loosely together. My tarp might be a little bigger. But then again the glass will not go anywhere if it is still in the frame.
It is better to keep it in the frame for there are sometimes little ceramic balls or just very dirty glass in the grooves that you don't want to get mixed into your good glass.
I use a very big sledge hammer used to hammer down fence-posts. A regular hammer is just as fine just will have to be use with bit more force.
Remember to have your safety glasses on and some gloves when you start peeling the glass out of the frame. but remember not to take to much more then where the glass goes into the groove or you might get some unwanted glass or dirt.
Carefully remove the frame from the main-body of the glass and take apart the frame after you have gathered the good glass in a bucket like this or what ever you have to store the glass. Put a lid on to prevent any unwanted dirt getting in there until you use it. Put the frame back on the tarp and clean the frame. They are usually out of aluminum and you can sell that to a metal scrap yard. Throw away the bad looking glass that comes out of the frame part.
Other sources of safety glass might be closer to you then you think.
Places that sell and buy metal get sometimes door and windows aluminum frames with the glass still in them. they will be happy to give it to you so they don't have to deal with it.
Glass tempering factories. They have mountains of broken tempered glass that they throw away.
Contractors often have to schlep away doors when they are fixing up houses.
Mention to people when you talk to them about your art that you are looking for safety glass and you will be amazed how many will happen to have a door or two in there yard or garage that hasn't make it to the recycle or garbage just jet
If you know of any other sources let me know. I will ad it to this list.