Critical components of this project are the Geiger tube and the 300V battery. The battery can be replaced by a small inverter, as the circuit current is few microamps. The circuit is from an old documentation. Transistors are general purpose types.
The Texas Instruments INA826S Instrumentation Amplifier Evaluation Module is available from Mouser...
May 2017 - Mouser Electronics is already in stock with the new BCP1395 transistors from Nexperia....
January 2017 - Mouser Electronics is shipping the new Littlelfuse TVS SP1043, SP1044 and SP1045...