You can buy one of the small ones with a maximum capacity of about 0.0003 mf.
"Letters of a Radio-Engineer to His Son"
John Mills
I should prefer the one of 0.0005 mf.
"Letters of a Radio-Engineer to His Son"
John Mills
You will need a grid condenser of about 0.0002 mf.
"Letters of a Radio-Engineer to His Son"
John Mills