If I correctly understand your question, you're seeking an internally geared 3-speed hub without a coaster brake. The answer is yes, Sturmey-Archer, Shimano, and SRAM all produce these IGH in various flavors. Some models may be too wide to fit your chosen frame, and if that frame is aluminum or carbon, you won't be able to spread the dropouts easily.
Buying the hub you want and custom lacing a wheel isn't too difficult to perform yourself, but it does take some materials and some skill. Bike shops like to charge for those things! You might find it's more... ahem... "fiscally responsible" to simply purchase the desired wheel assembly from the get-go.
You do realize that by foregoing the coaster, you'll need to arrange for another way to stop, right?