I remember seeing a Nixie tube on Ebay while i was searching for something else and a quick Google revealed they were used to display digits in early calculators and calibration equipment. After a period of being neglected someone had the idea of using Nixies in a sort of retro clock. While the larger tubes can be very expensive, some of the more common smaller types can still be found at reasonable prices. Designing the board was beyond me so i went the easy route and bought a kit from Nixieclocks
On Ebay i sourced my own tubes using the ITT GNP-17A tube for the Hours/Mins and smaller Russian made IN-16 for the Seconds. After some intial confusion with the GNP-17A tube pin-outs the whole thing went together in an afternoon..