I'm another vote for Rotometals. I got some 1/64,1/32 and 1/16 years ago in a 3'x1' sheet and still have most of it. I think this amount constituted a lifetime supply . . . I use 1/32 more than anything else, although I've been known to "line" the floor of flat cars with 1/64 to give them more weight (you can then take a sharp #11 hobby blade and scribe small lines in the lead sheet, paint it, and it looks like wood plank when you're done). Lead makes an ideal speaker enclosure because of its weight and inert nature (it doesn't vibrate). It's also easy to glue with CA cement (I use thick CA for my speaker enclosures, which also helps fill any tiny gaps). The only problems are that (1) it is toxic (you want to use neoprene medical gloves or something similar when working with it, and for God's sake, don't sand it!) and (2) it conducts electricity, so you have to be careful where it goes. On the Knowles Dumbo, for example, the speaker leads are at the short ends of the speaker. If you use lead sheet on the short ends, you risk shorting the speaker if you also use lead as the speaker bottom, because the bottom will "bridge" the two ends. I sometimes use 1/32 sheet for the long sides and .030 or .040 styrene for the short sides, along with 1/32 on the bottom. More often, however, I use .040 styrene for all the sides and 1/32 or 1/16 lead sheet for the bottom. On a speaker the size of the Dumbo, using lead sheet for just the bottom of the enclosure adds considerable weight.
John C.