I think you'll find acetylene gas almost impossible to source - it's been totally replaced by LPG, as to oxygen - a call to your local Air Products or BOC depot will get you the info:
For welding?
In the end many people give up, it was always a dreadful monopoly and you generally get involved in bottle hire which is extortionate.
Let us know if you find anything has changed.
Replaced my full size bottles last year. About £130.00 for the gas plus monthly bottle rental. I prefer Air Products bottles- they have on-off wheels on the bottles instead of a loose key and I have a local depot where I can collect. Air Products used to be flexible on bottle rental,no annual contract.
I buy my gases from Bumble Bee in Connah's Quay 01244 818187. Much cheaper than the big suppliers as there is no rental involved, the cylinder is bought outright then exchanged when empty.
If actually gas welding, as opposed to cutting or heating or brazing. Then LPG is not the stuff. Acetylene forms an inert shield around the weld, the others don't. If cutting or brazing hydrogen is cheaper.
DW