Where can I buy item for honeywell wv8840a gas control valve

https://www.lowesprosupply.com/Catalog/Water-Heaters/Water-Heater-Parts/Gas-Valve/GAS-VALVE-FOR-AO-SMITH-WATER-HEATER-702210Looks like a good place to start.
Plenty on Amazon and Ebay but I wouldn't buy them from there.

replace valve

Gas valve might be bad...
The honeywell gas valve for atmospheric models is generic and can be replace without removing from heater.
Following links have resources:
http://waterheatertimer.org/How-to-replace-Honeywell-gas-control-valve.html
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html#honeywell

That's an atmospheric vent gas water heater with Honeywell gas control valve thermostat
Following links have information, error codes and troubleshoot manuals:
http://waterheatertimer.org/Honeywell-gas-valve-blinking-4-times.html
http://waterheatertimer.org/troubleshoot-gas-water-heater-thermostat.html#thermostat
http://waterheatertimer.org/How-to-replace-Honeywell-gas-control-valve.html

Google for "Vr8204c 1084 manual" ... 1st item says:
http://www.warming-trends.com/manuals/HoneywellTroubleshootingGuide.pdf

68-0047 - VR8204; VR4204 Intermittent Pilot Dual Automatic Valve Combination Gas Controls

Pretty much chapter and verse - you don't usually get any more.XV66OI
This is an industrial valve. Are you safe to meddle with it?

Replace the gas valve?
http://waterheatertimer.org/How-to-replace-Honeywell-gas-control-valve.html

http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html#intellivent

Gene

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

Copy following links:
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html#intellivent
Build-up of un-ignited gas sounds like gas control valve problem
WV8870 is power vent gas control, but replacement is similar.
http://waterheatertimer.org/How-to-replace-Honeywell-gas-control-valve.html
http://www.thetankatwaterheaterrescue.com/forums/forum3/

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

Copy following link to troubleshoot by type of gas control valve, and read how to replace gas control:
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html#intellivent

There are basically two types of Honeywell gas control valves.
One for atmospheric-vented water heater, and one for power-vented
For both types of controls: 8 flash + 3 flash error: replace gas control valve.
Water heater does not need to be drained to replace this gas control.

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

Troubleshoot by type of gas control valve
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html#intellivent

Repeated 3 flash on power vented honeywell gas control thermostat means system in lockout.
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html

Repeated 3 flash on atmospheric-vent Honeywell gas control valve means temperature sensor failure.
Take apart gas control, and buy temperature sensor if sold separately at AO Smith dealer.
http://waterheatertimer.org/How-to-replace-Honeywell-gas-control-valve.html

Add a comment with more information

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

Whirlpool is made by American water heater.
Gas valve is made by Honeywell.
Whirlpool electronic control is version of Honeywell 'Icon' gas valve: There are several versions of this gas valve.

http://waterheatertimer.org/pdf/Bradford-White-service-manual.pdf
Start page 24 shows: Testing, disassembly and replacement of typical Honeywell gas valve.

Whirlpool phone number 1-877-817-6750
Whirlpool manuals:
http://www.whirlpoolwaterheaters.com/support/manuals.aspx