Depending on your vehicle type you may have either gas bottles or gas cannisters.
Gas bottle
The gas bottles can be refilled at any location that offers a refill of LPG gas. Depending on your location, it may be best to do a quick internet search for "LPG gas refill near me"
Some vendors may offer a swap and go service, however the size of the bottle may not match the bottle you already have. Just make sure you check the size of the gas bottle before using the swap option.
Sample image of the gas bottle for reference: (not to size or scale)
Gas Cannister
You can purchase new butane gas cannisters for your portable camping stove from Kmart, Bunnings, Mitre 10 and or any other camping store (such as BCF, Anaconda or Kathmandu).
Sample image of the gas cannisters for reference:
