Workstation Class PC laptops are still being made with ExpressCard slots. There are many great refurbished options that have ExpressCard options as well. The misconception is what is being seen with 'new' laptops.
Mac's have had Thunderbolt 2 ports for a few years now. The Thunderbolt 2 to FireWire 800 does work and is supported. Very few aftermarket PC motherboard brand's have had TB2 ports, so experience with those is limited, but mostly with success.
Thunderbolt 3 uses a different connection type, USB-C, instead of the Mini Display Port like TB2 did, so there is no TB3 to FireWire adapter officially supported, or made at this time. You will need to use Thunderbolt 3 to Thunderbolt 2 adapter, then Thunderbolt 2 to FireWire 800 adapter. 2 adapters. This should work, although we have not fully tested on PC at this time.