I work for Airgas and might be able to shine some light on your situation. Your oxygen cylinder is what Airgas calls a 200 size. As for the correct acetylene, the military uses a couple of odd sized acetylene cylinders. One size is called an AC 4.5 (by airgas terminology) and it is shorter and fatter than the standard 4 (or some call them a w/s). The other size that I have dealt with are #5. Not overly common but they are out there on the mobile container shops that are hauled by the hemmts. On rare occasions we will have the national guard and reserves give us their empties to be sent off for refill (they do not exchange due to their cylinder ownership and asset tracking) The #5 will be available at many airgas facilities if they have customers that use them. Due to the size and weight (think they tip the scales at or around 200#) most industries don't use them. As for the 4.5 they are pretty much exclusive to the military and various federal agencies. If you are wanting dummy cylinders, talk to you local branch and ask them to contact their fill plant/and or their acetylene plant. Many times they have cylinders that did not pass hydro test and are awaiting the junk yard. There is a pretty good chance the acetylene plant will have some old 4.5's that did not pass. They are normally de-valved and may have other permanent destruction done to keep them from being used, same way with the oxygen cylinders.