To buy Petanque equipment it is best to go to an online shop. A brick and mortar Decathlon in North Harbour carries some petanque stock, but it is extremely limited.
There are two types of boule. Leisure Boule (only for club play), and Competition approved boule (a must for competitive play, and recommended even for club play.)
Leisure Boule can be bought at mainline online retail outlets like Amazon and e-bay as well as the outlets listed below. Leisure boule can vary quite a bit in quality so please be careful if buying them. Generally, if you can afford it you are best to buy competition approved boules for a number of reasons. More information about this in Boules.
Here are the usual online suspects:
Decathlon Is the cheapest shop to buy boules. However there is a very limited range of sizes, weights and patterns. The problem with buying boule here is that there are already club members who have snapped up the cheapest (perfectly fine) competition boule and it is best to have a boule you can distinguish as different. If price influences you heavily go with Decathlon but have a look at other club members boule and try to get something different.
DC Petanque Started as an ebay shop and has expanded into it’s own website. DC carries a fairly good selection of boule at competitive prices, and there is a good range of sizes, weights and patterns,
Pen Y Coed Petanque These have been around for years. They have an actual shop that can be visited (unfortunately nowhere near Portsmouth). If you are wary of buying online then this is the place for you as they take orders over the phone. They are a bit pricey, mitigated a touch by free postage, and a bit more by the fact you can ask for advice when ordering as you will be chatting to them on the phone.
Petanque Shop (French) Although these are French I mention them as they have a massive stock of boule and other equipment way beyond the three above. The link is to an English language website. Depending on the value of your order the high postage charge can be offset by the cheapness of the price if the euro exchange rate is favourable. Probably a bit expensive right now given brexit and the subsequent lowering of the pound but definitely one to check out.
Others. There are occassionally other small boule internet enterprises that come and go, usually set up by by petanque players. So keep your eye out and search on the internet just in case.