This is the biggest geiger tube I have seen! I’ve bought one for 25€ at eBay.

Glass tube, thermostable. Cathode: tungsten powder.

• Length of the plateau: not less than 200V
• Slope of the plateau: 0,07%/V
• Recommended working voltage: 900V
• Dosimetric characteristics N = 0.1 imp / min · cm2 at 1 microR / s              Nmax = 2 · 104 Nf = 31
• Service life: impulses 5·107
• Range of working temperature: +10 / +250 °C
• Dimensions: ∅27 x 400mm 92g