Bits for this

[Millsy 82]

Anybody know what make this is so I can get a new sight tube for it and new o rings for the sight button.

 

[Best]

Try looking at this. It seems same thing & I see you can click on a link for spares. -

Atkinson Tankmaster Valve

You might find that the sight tube is same as you can buy in a roll for standard sight gauges & cheap enough.
O rings might be better the exact type from the manufacturer.