AMD has had issues with adequate supplies of the R9 3900X from the launch onwards. The lower price bins are also largely not in stock either.

We are focusing on meeting the strong demand for our 3rd generation AMD Ryzen processors in the market and now plan to launch both the AMD Ryzen 9 3950X and initial members of the 3rd Gen AMD Ryzen Threadripper processor family in volume this November. We are confident that when enthusiasts get their hands on the world’s first 16-core mainstream desktop processor and our next-generation of high-end desktop processors, the wait will be well worth it.

The 8 week wait is intended for foundries to make more wafers and tape them out for packing.

AMD Ryzen has much been more popular than expected and supplies are not keeping up.