As well as existing gold coins there are also the regular issues of new gold coins. Various mints such as the US Mint, the Royal Canadian Mint, The British Mint and many others issue BU (Brilliant Uncirculated), proof and commemorative coins yearly.
Canadian Maple Leaf gold coins from Canada, Britannia gold coins from the UK, US Gold eagles, South African Krugerrands. Pandas from China and Kangaroos from Australia. All are produced on a regular basis.
One can buy single coins but, if you can afford it, it is better to buy about 5 ounces at a time in gold coins as the mark up, handling and shipping charges by the dealer is going to be a lot less. Sets and presentations of gold coins are a good buy also.
If possible find coins that have a limited mintage as these will increase in value over the years since there are only a limited number made.
When buying gold coins always ensure that you deal with a reputable dealer and ensure the coins are what were described, when you receive them, especially when it comes to the condition. If you buy proof coins they should be proof and not BU. If you buy BU they should be BU and not simply uncirculated.
Check that the coins are properly sealed and have not been opened and resealed again. They should be sealed in a plastic transparent container especially for proof coins. Proof coins usually come in a presentation case or box. That presentation case should be the original, not a later made up one. You can check this by going to the mint and checking how the coin was originally sold.
Some mints will sell coins direct to the public and this is a good guarantee that you are getting what you asked for.
Buying new gold coins can be fun as well as a good investment for the future so it pays to ensure that you are getting what you paid for.