[Boatanchors] replacements/substitutions for 8873 tube?

[Eugene Hertz]

hello all, 

been considering getting a heathkit SB-230 linear amp, but I understand the tube it uses is difficult to find. I was wondering if anyone knows of a replacement or substitution that might be more available? Or whether anyone has designed a modification to the amp that could allow it to use a different tube? 

thanks 
Eugene 
PS I am not a member of the heathkit reflector otherwise I would send there too