I personally need spring 'verb in my amps but you're gonna find that adding it to an existing amp that doesn't have it is gonna be more than you can do unless you're an electronics guy, in which case you wouldn't be asking about it. It would require adding circuitry to the amp.
Better to just get a pedal with a spring 'verb setting if you're gonna use it live.
If it's just for recording then use the 'verb plug ins or whatever hardware FX you have.