You might consider saving your own seeds. It's not too hard. Though hybrids might not be possible. 
I tried San Marzano and they didn't do good for me. I find if I start my own plants I have better luck. 
I'd decided once that to buy plants was easier than starting them but one year everyone got hit with a blight that was said to have come up from the south on the plants. 
We have local growers who start them up here.  Still I will start my own. 
So far the seeds I've got are.  Bonnie Best, Homestead and St. Pierre.  These are the canning tomatoes I plan on growing. I'll grow others for eating, though I've been known to can anything.