If you're after designer swimwear, www.biondicouture.com is your best bet
Otherwise JD sports, JJB sports all stock everyday swimwear along with specialised shops such as Speedo in Covent garden
One can purchase Polo brand swimwear in the Polo store physically, in the Polo store online, in eBay and in any store that sells these swimwear such as Old Navy.
Many specialty stores offer swimwear year round both online and in store. You many also be able to find swimwear year round by going to your local YMCA or gym.
The easiest way to find the nearest swimwear sale is to browse through your local Sunday paper's sales ads. If a store is having a sale they will publicize it there. You can also call stores closest to you and ask do they have any swimwear on clearance.
swimoutlet.com offers swimwear for every size, including plus sizes for toddlers, and you should be able to find cheap prices for them too. If you want a more specific department store instead of a generic website, then you could try the Gap, which also has a wide selection of swimwear.
Roxy swimwear can be purchased directly from the Roxy online store. Many other stores stock Roxy swimwear, such as Macy's, Sear's, Debenhams and Amazon.
A person can find a variety of maternity swimwear at maternity shops. One could also find maternity swimwear in the maternity department of department stores.
Costco in Canada does sell plus size swimwear. They are very limited in their plus size styles so it is usually best to find a specialty store such as Lane Bryant.
One can find maternity swimwear from online sites like Amazon or eBay. One can also find maternity swimwear from retail stores like Target, Wall Mart and many more.
There are a few places where you can buy Jets swimwear. There are online stores where you can purchase the swimwear such as the Jets official online store and Surf Stitch.
Old Navy has swimwear for babies ranging from 0-24 months. I found this super cute bathing suit on their website, http://oldnavy.gap.com/browse/category.do?cid=54738
Depending on how overweight your toddler is you could go to a big dogg store. There are some great websites that you could browse such as gap.com, jcpenny.com, target.com. Maybe you could try a small childs swimwear on him/her.
Miraclesuit swimwear can be purchased at Belk, Bloomingdales, and Land's End. You can shop at these retailers online or in a retail store location nationwide.