I am also looking for a Thundelbolt 3 NVMe PCIe SSDs external enclosure.
Your topic of discussion has been the basis of my research, so I decide to share the result of my research.
Here is interesting list of all external enclosures certified by Intel (Thunderbolt 3 for SSD NVMe PCIe) https://thunderbolttechnology.net/sites/default/files/thunderbolt_3_product_showcase_2018_Q4.pdf
Manufacturer link : http://www.win-star.com/eshop/goods.php?id=225
Here is the external enclosure sold without ssd that i found at the best price https://french.alibaba.com/product-detail/Winstars-Patent-design-Aluminum-Type-C-60779539843.html (50 to 64 USD, minimum 5 pieces to order)
Personally, it's just for the BackUp, the support is clearly overkill. But as I have a Samsung 970 EVO 1TB SSD stock, which I do not use, and as my laptop to a port Thunderbolt 3 (ThinkPad T480S), as much fun (as far as the price is reasonable)