Intel plans to ship X38 chipsets to its customers who are willing to pay in advance in week 34 the one that starts on 20th of August. This means that a lot of good paying customers will have the chance to make the golden samples of the first X38 motherboards in last days of August.
The be more realistic the guys who paid unit today middle of week 29 and the chaps that will book latest in middle of week 31 around first days of August have a chance to have a prototype boards in late august.
The real production in volumes starts in early days of September and I guess a lot of Taiwanese based motherboard manufactures will have to fly the motherboards in the US and Europe to have them ready for planned Q3 launch.
If you want X38 based motherboard you will have to wait until September and if you cannot wait get yourself P35 as there are quite few of good motherboards based on this chipset.