Here are some of the bits I got, all are eBay item numbers:
Banjos: 132813620405 You need 6mm hose ID for both, 1x M10 and 1x M8
T piece: 264393424153
Valve: 283550283654
Hose: 140850656095
Hose clamps: 222439718697 10mm-12mm size fit the hose above
That will make up everything you need apart from the actual gauge. I used this: https://uk.rs-online.com/web/p/analogue-positive-pressure-gauges/2473602/
They do the same gauge without calibration for 55 quid less and I doubt they do anything to them apart from test and supply a certificate https://uk.rs-online.com/web/p/analogue-positive-pressure-gauges/2435919/