Buffer tanks...

[Laser]

Worst case scenario. I could create one perfect fitting from Ti tube and end plates.

That may be a tad too expensive

How long do you want it?

about 250mm but around 0.5l volume

[Max]

I've got one here, about 0.85l volume, 230mm long in total (19cm without fitting) 70mm diameter. Working pressure 14bar with a 1/2 thread
Pm me if interested

[maddox10]

That may be a tad too expensive

You never know, a search on Ebay could yield you the right basic stuff.
Welding it up ain't that hard.

[Laser]

Ill have a look at the scrapyard and see what they have, if not Maddox your option would be ideal