Jensfic
Since you have not received an answer perhaps I can provide some insight.
The OP wants old SCUBA tanks to convert them into SCUBA bells and or Regulator displays.
Most, but not all SCUBA bells are made by using a metal chop saw to cut off the bottom of the SCUBA tank, install as attachment device on top and a bell clapper internally and presto! A SCUBA Bell.
You can see a partial view of one that sets in our foyer ..Go to "WWWportagequarry.com "legends of diving" Orange County did you know?
There you will see a picture of me, Pat & Cindy Smith with one of my wife's bells in the back ground
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Cut off the top ( where the Hydro stamps are located) and presto! a regulator display for a SCUBA (dive) Shops and collectors.
( I was the LA Co Outstanding UW Instructor in 1969 and one of my awards was a gold plated 2 hose regulator which I have mounted on the top of a SCUBA tank top setting on a shelf behind me- and where it has been for over 25 years)
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As the LA Co Underwater Instructors Association did so many years ago cut 38s, 42s etc length ways install some hinges, a handle and a grate and Presto! A SCUBA Bar B Que. They made a number of them and sold them for several years at the SCUBA Show, ( Now in Long Beach)
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I. my wife and many of our friends have been making SCUBA bells for --gosh 35 perhaps 40 or more years.
There is considerable more work than just cutting the bell .....over the years we have experimented with all sorts of ways to camouflage the external appearance of the bell to convert it into an acceptable piece of art , to create numerous methods of attachements, and of course all sort of clappers to soften and often change the tone of the bell. And now we are experimenting with aluminum and beginning to get great tones out of them.
Mrs Miller and I have been fortunate to have been engaged in diving for many years,me since the 1940s beginning with googles, my wife for over 50 years beginning with double hose reguators, as one would imagine our home is a combination of a home and a diving museum with all sorts memorabilia past adventures and 7 SCUBA bells , 1 in the foyer, 2 in the living room and 4 out side as lawn art.
As a young spearfisherman recently said as he walked in "So this is what a real divers home looks like !"
I hope this explains the reason for the OP wanting used SCUBA tanks .
Save your condemned tanks or rush over to your local shop and grab a few to make your own SCUBA bells or even SCUBA chimes
SDM