I'm attaching a link to the supplier I use. I don't see the size you're wanting online but perhaps you could call them. They carry products from multiple manufacturers. If you knew who made the trays you had that would help. 4" is a pretty deep container. I don't know if I've seen a tray that size, but you never know. Good Luck.

Here is a link that might be useful: Propagation Trays/McConkey

Thanks.
The reason I ask this, is because I gave a few to a friend and He liked them. They are large enough to take seedling plants all the way through the 8 week starting period and gives plenty of room for the roots. He uses the 3.25" x 2.25 x 2.25, but was wondering where I got these. I have no clue and can't find more.
Dave

Have you tried folks who sell to the tree nurseries? They have particularly deep starting trays. You could search under "Silviculture" or "forestry" propagation supplies.

http://quickstartgardensupplies.com/index.cfm?fuseaction=category.display&category_id=23
The URL above is for the styrofoam starter trays which I use and they work real well. They don't have the break apart cells, but the plants pop out easily.

Our greenhouse guy, at school, had some deep ones last year that were used for starting trees because of the depth. He is gone now but I will try to locate one to see if it has a name on it.
paws