I can provide aircraft spec cylinders with appropriate paperwork but they have to be fitted by an LAE. I can't supply fitted O2 systems only portable.
As far as the comments about what you can and can't fill. Most filling stations will fill a cylinder without checking it, this does not make it legal. I will fill any cylinder that has in date test on it. The IDEST regulations for 2007 and technically do not permit us to test non European cylinders nor fill them. As an interesting point as well we are not allowed to sell non European marked cylinders either. The establishments that are selling them are doing so because they are below the radar. All cylinders actually only come from a couple places, cressi sub makes cylinders in Italy and the others are US based, Luxfor, Hydrotech and Carleton. Carleton make all of the Carbon Fibre and Kevlar cylinders. The carbon cylinders are the preferred option in aviation as they are light and have high working pressures.
The other advantage of using Euro cylinders is that they are 230bar working pressure and will be filled by a SCUBA shop. I can fill O2 to any pressure as I have a Haskel pump that will produce working pressures of up to 400bar. Most technical diving shops have the same set-up. I also manufacture DIN477-9 and CGA540 to DIN477-6 adaptors so that the cylinder can be filled by dive shops. Getting a fill at a dive centre with a strange non Euro cylinder can be hard work. Getting a CE marked cylinder with the correct adaptor is easy.
Filling O2 cylinders is not for the untrained, the SCUBA industry has had it's fair share of accidents when it comes to O2 and air filling. If anyone wants my slide set that I use to teach O2 filling then please PM me, it has some great shots of corpses from those who got it wrong. The best one is of the skin of a guy hanging from a washing line.
There is also the thorny issue of using welding gas. Yes welding gas comes from the same tap as all of the other grades of O2 but thats where it ends. Welding O2 is put in any cylinder that is handy, the cylinders are not vacuumed before filling and the quality or moisture content is not certified. Some will so well they are just refilling what already had O2 in so whats the chance of contamination? Actually what happens is they take any cylinder that is available when they run short and re-spray them to O2 markings and fill them. Aviation grade and Diving grade are the same grade and go through strict quality control. Medical grade is the same but often has the moisture content increased to make it easier on the patient. This moisture is not good for the HP seat on the 1st stage or the solenoid valve in things like the O2D2 kits.
Home filling is an OK solution provided you seek some training on gas handling but it is also a very expensive way of doing it especially getting cylinders from BOC who are one of the dew places that will rent cylinders to individuals. The starting pressure barely makes 200 bar whereas places like Lindi/Air Liquide supply at 230bar and then after a few top ups the working pressure drops. Cylinder rental is expensive as is delivery. Storage of compressed O2 requires notification to you insurance company and the local fire service.
As far as kits go I have several here. The one I have had most success with is the O2D2 unit from MH. They are reliable and very efficient, much more so than the DAN or Aerox kits that I have. Yes the do fail shut but not really a hard ship. The beauty of the MH system is that you can plug any of the kits into the first stage. So I carry a couple of spare flow meters attached to the spare ports of the 1st stage. If the O2D2 failed I would just swap over. At GA heights we have plenty of time!!
The aerox kits are also good, they are reliable and simple to service, but the use only low pressure seats in 1st stages so are a max 137bar fill, this means bigger heavier cylinders for the same gas duration as the O2D2. aerox generally come with a CGA540 thread not a problem as we have CGA540 valves on Euro Spec cylinders and adaptors for filling.
Whilst I am all for overcoming the system of useless bureaucracy that the Europeans force on is one thing I would add is that making a mistake with O2 will cost you your life. As a closing story, I had a friend whose Closed Circuit Rebreather which has an O2 system built in pressurised it too quickly created all three sides of the fire triangle instantly and the 1st stages caught fire (YES METAL BURNS!) and set the unit alight and then the boat.....