For both the Cancer and Geminin swimsuits, you could find some appropriately colored fabric at the store (Nylon will probably work, but Spandex/Lycra is a common fabric used for swimwear as well) However keep in mind that both fabrics have their pro's and con's.
Nylon = Has a lightweight, smooth fit and dries faster than the other materials but has poor resistance to prolonged sun exposure
Spandex/Lycra = Has excellent elasticity that offers a slimming, form-fitting feel and can also be used in combination with other fabrics, but does not hold up well to chlorine
(You can go here for a little more info http://www.moreswimsuits.com/swimsuit-fabric.html
Here is a good base pattern that you can edit a little to your tastes.
Hope this helps some!