Igniter for potato gun

Looking to make a 30k Volt igniter powered by 9 volt battery for my potato gun. I have been using a BBQ Grill igniter looking for something a little more reliable

The BBQ grill igniter should be almost perfectly reliable, if it's acting flakey on you clean the contacts with a good degreaser and then wipe it clean, make sure you have bare metal as close as possible from the ground lead to the spark discharge terminal. Any batter powered option will be more failable than the igniter you currently have. If you've fould the one you have badly enough you may simply need a new one, and remember to clean it after a few uses Potato guns tend to generate a lot of soot depending on the gas used for ignition.

Use a good quality sparker unit with a lawn and garden engine spark plug. They have very low internal resistance, 10's of ohms, in comparison to automotive spark plugs, 1000's of ohms.
With a good grill sparker and a properly gapped plug you can get a good spark capable of igniting any correct A/F ratio within reason.