Check in the Utility Bike Forums for one place.

If you specifically want a bike similar to that, the simplest way to do it is keep an eagle eye on Craigslist and watch for a Worksman Front-Loading Tricycle. They show up periodically, so it may take 6 months. They are not necessarily as high quality as a dutch bakfiets-type bike, but are usable. The platform on the front of them just bolts onto the springs with 4 bolts, and you can build any kind of box you want to and bolt it on there. They are usually single-speed, and you pretty much need to live some place flat to use them. You want one with with pneumatic tires, not the solid rubber kind, and you want the original wheels if possible, which are extra-heavy-duty. These trikes are around $1,000 new, but often go for $200 or so used- they are very low supply, and very low demand, so prices are erratic.

Have you actually used one? They are cool, they do have some disadvantages- such as being slower, much heavier, and catching more wind. If you're figuring to ride 10 miles each way every day, get a regular bike. If you're going a couple of miles to the store, these things work. If you ride in the road, you pretty much take up a lane whether you want to or not, so pick your routes judiciously.

I believe there is also a Haley trike in the northeast that custom-makes similar trikes.

One challenge is that the front wheels on the Worksman trikes use an axle which is not used on a standard bike, so you have to come up with something different there. On the other hand, the Mexican cargo trikes are set up to use standard bike wheels. Google up Mercurio or Husky cargo trikes to see what I mean.

You might look up the Atomic Zombie stuff. They have a bunch of do-it-yourself plans for odd cycling contraptions, and may or may not have a functional equivalent to this.

Local junior colleges may have welding classes, if you are interested.