Why in the world would you buy chains?
Unless you have an XRF machine, are you even going to know for sure that you have got whatever carat gold chains or if they are even solid low carat gold - there is a massive market for fake gold, just look at ebay.
I don't buy bars either as they are not CGT exempt, which matters in the long run.
Fractional gold coins or full oz coins do not attract Capital Gains Tax if they are issued by the Royal Mint with a value in legal tender and are fairly low in price if you can't buy by the ounce which is the most cost effective way.
Just search for CGT Exempt coins.
A 1/10th oz Britannia or Royal Arms is about £280 at the moment, or a 1/4 oz is about £650 (maybe a bit less if buying best value stuff).
I mostly use Chards (Blackpool based, they have a YouTube channel now if you want to see Lawrence Chard talking about coins at length - the guy knows his stuff) or The Royal Mint, but there are other reputable dealers out there.
No dealer is going to be selling for spot and I'd be wary of anyone who was.
The margin over spot is their income which needs to cover business running costs and profit as they tend to pay around spot and they are not a charity.
They tend to pay around spot for bullion and if you are not buying bullion you are gambling with the massive mark up you will have paid on special edition stuff unless you are very knowledgeable and lucky.