Intel rushed Coffee Lake to the market ASAP because they wanted to stop the marketshare hemorrhaging from Ryzen 5 and 7. They didn't take bother take the time to built reserves and stock for a public release. I expect Coffee Lake SKUs to be difficult to obtain until Q1-Q2 2018. It also appears that current batch of 4-core 8 series chips are actually rebrand and repackaged Kaby Lake silicon (only work on 3xx series boards) not binned Coffee Lake silicon. It does easily explains their general availability versus nearly-unobtainable 6-core SKUs.
Ivy Bridge i5-3570K@4.0Ghz, Gigabyte Z77X-UD3H, 2x4GiB of PC3-12800, Sapphire RX Vega 64, Corsair CX-600 and Fractal Refined R4 (W). Kentsfield Q6600@3Ghz, HD 4850 2x2GiB PC2-6400, Gigabyte EP45-DS4P, OCZ Modstream 700W, and PC-7B.