Assuming you want 6 volts. Here is one on Amazon.
Available from other vendors as well. My '39 p/u is 12 volts but I run a 12 volt Airtex just to prime the system after it sets for a while. Bought it at the local parts store but its a real parts store not a big box no nothing one.
https://www.amazon.com/Airtex-E8902-...24355167&psc=1