Pretty much everywhere I've looked is either listed as out of stock or back-ordered, which I presume means the same thing (no one actually has them yet). A few places have release dates of August 1st, so end of July kind of tracks with that. Sucks if they are producing the lower mem models first. I'll be very surprised if those outsell the 4GB models when they are all available. I was tempted to try and order a 2GB model, but I really want 4GB (so I ordered two of those).
Now if I can just find the strength to be patient...
Looking on the bright side, maybe by the time the 4GB is available most of the early release issues with Raspbian Buster will have been fixed.