Yup, there are no 40 amp continuous batteries on the market right now and I suspect when that technology is developed it will come from one of the big players like Sony or Panasonic.
If you need 30 amps, RDT Vapor has
Xtar branded VTC4's in stock. I understand they are a bit longer than normal. OTOH, I'm also using 25R's and HE2's down to 0.3 ohms in mechanical mods and they are doing just fine.