Radio Shack or an electronics store would be the first places to check
The batteries you are looking for can be purchased anywhere and do not need to be special ordered. Some retailers I know of are Radio Shack and amazon.com.
can a 12v lawn mower sealed battery be charged with 12v battery charger use on cars
Anything needing 12V to operate.
12v, 3.3v 5v
12v
No, you need at least 12v to charge 12v. Most alternators charge at 13-14 volts.
The battery is a 12V car battery.
YES
DC 12V power supply can convert 110/220V AC power source to 12V DC.
if you have 12v dc then you can use a 4 ohm resistor
Battery chargers have a 12v DC output.
12V 5A = 12V 5000mA