I got our chromadepth glasses on amazon. We use the paper ones and they were about $1 each. We only have around 50 kids each year and I pull out 10 new pairs to use through the night, so it hasn't been too hard to keep track of the glasses. We have the kids walk through the chromadepth tunnel first and then return the glasses at the front door to get their candy. So far we've lost about one pair a year, but I do make an effort to keep track of them and ask kids to return them. I don't think any of the glasses would come back if I didn't do that.
We usually lose about a dozen during the night. It's the little kids who usually slip them unknowingly in their TOT bags.
We buy ours on Amazon, but I modify them. Of course patrons at pro haunts do not have TOT bags or accessories, such as swords, hats, wands, etc. I've found it easier for my home haunt to cut off the ear pieces. Then I attach a paint stir stick on the side of each glass, like a monocle. I also decorate the glasses in that year's theme. The TOTers then can hold the glasses up to their eyes, even if they have masks, wigs, etc. They are easier to collect that way as well. I usually just swipe a few sticks each time I'm at Home Depot.
We used them at the Rocky Mountain Haunters booth at Salt Lake Comicon. I don't know the source of where they were bought, but we lost a few pairs through the night. For some reason, folks just think everything on a table is free. We had to tell about 1/10 to give us the glasses back. The rest just looked and handed the glasses back on their own. We had some cool props their, but I'd say the chromadepth paintings were the big hit.