Here's a place you can get them.
Here's what they look like.Here's another discussion on the topic.
First things first. Edgie Wedgies are a tool to be used when needed. I always have one in my pocket when teaching. I really like them for use with specific students.
Second, when attaching them, put the screw down. This way it bites into the p-tex. It gets a good grip on the ski tip and doesn't scratch or mar the surface of the ski.
As Weems said in the referenced thread, kids develop at different rates. They develop gross and fine motor skills from the top down and from the core outward. Thus you can have two kids that are the same age and yet one kid can make and hold a wedge while another has problems.
All an edgie wedgie does is help keep the tips together. As an adaptive instructor, I've used all types of ski bras, trombones, and edgie wedgies. I prefer the edgie wedgie for a multitude of reasons. It does not "lock" the hips in one place like a ski bra does. (When you hold the tips rigidly together, the kinetic chain prevents the hips from moving independently.) The elastic of the edgie wedgie allows the ski tips to move in and out a bit which mimics the movement of the skis without it attached. Also, if you watch the edgie wedgie for slack, you can get an idea of when the student is ready for it to be removed.
As with all tip retaining devices, keep a close eye on your student to insure they don't go backward. This could lead to a split. Normally the edgie wedgie will pop off or stretch before it becomes a major problem. (Unlike a metal ski bra.)
I sometimes trick my students into realizing they don't need them. I'll reach down to "tighten" one of the clips. (Actually I loosen it a bit so it will slip off easily.) As the student skis the clip pops off. They normally don't notice it. When we finish that run, I'll point out, "Wow, the edgie wedgie popped off and you kept skiing. That's great! Let's do it again!" Of course if it pops off at another time and they keep skiing, I'll do the same thing. Use everything to your advantage that you can.
So, use it as it is meant to be used, as a tool and not a crutch.