What about
:
https://brimaruk.com/valves/rectifiers/brimar-gz34/
Or
http://pmcomponentsnos.co.uk/Golden-Dragon-5AR4-GZ34
To be honest, it's just a rectifier valve - don't get uptight about particular brands/bottle-shapes/getter-positioning etc being 'better' than others; honestly, I'm sure that if decent/cheap/reliable semiconductor rectifiers had been available when your amp was designed the designer would have used them!