Denford Triac VMC with ATC Conversion / Fix

[m_c]

RS are expensive for pneumatics, but they're mostly supplying repairers who will pay extra to get a machine back up and running quickly. Parker are also expensive if you're paying full price, but machine builders get quite big discounts, which is why they're so popular.
.
Try the Norgren catalogue to see if you can match the cylinders - http://www.norgren.com/uk/info/12/actuators
Once you have a part number, try googling it to see who can supply it. I've not used pneumatic actuators for a long time, but the hardest part was always identifying what you need.
.
There is a possibility the threads could be imperial, so could be worth investing in a couple sets of imperial and metric thread pitch gauges, as pneumatics/hydraulics still use quite a bit of imperial.