Are you looking for the regular 18s or the Express 18s? I personally prefer the Express 18s. They are made from a much heavier plastic and can be reused pretty much indefinitely. The regular 18s are made from a more brittle plastic. You will get a few reuses out of them. The Express trays each cell can be lifted out of the slot and moved around. The regular 18s have cells in a fixed position. I find that many trees grow at different rates. I like to use inexpensive florescent shop lights that are cool and can be hung on cords with prussic knots and adjusted so they are only a few inches from the trees. The express trays let me reorganize trees as they grow. I can put taller trees on one end of the trays and shorter on the other and adjust the shoplights at an angle so they are roughly the same height above all the trees. With the regular trays you can really do this.
John is a great source. He can let you know what he has in stock. I just want to make sure you know the difference between the trays. The express trays are more expensive but worth it in my opinion.