Well looking on OCUKs site there seem to be a few in stock 9/14 listed are in stock and / or brought to order workstation ones and some of the out of stock ones like rampage extreme omega from elsewhere readily.
As to why not so many options, well I doubt x299 sell in massive numbers, what with the mainstream CPUs encroaching from the bottom and threadripper to an extent putting some pressure from the course count perspective.
Doesn’t not make as much sense for mobo vendors to bring out new models as most already out cover everything I expect already.