The French Knoppix site, http://knoppixfr.tuxfamily.org/, has translated their hardware database into english: http://knoppixfr.tuxfamily.org/index.php?page=hardware There are not a lot of listings yet, and the site surely doesn't reflect the large amount of hardware that works under knoppix, but hopefully it will grow.
Fortinet FortiGate-40C Network Security Firewall
$37.50
FORTINET FORTIGATE-80C FC-80C NETWORK SECURITY FIREWALL APPLIANCE
$42.29
Ubiquiti Networks USG Unifi Security Gateway Router/Firewall
$29.95
NetGate SG-2440 with pfSense Plus Console GNU Router Firewall Security Appliance
$69.99
Fortinet Fortiwifi 60D FG-60D Security Appliance Firewall / VPN w/ AC Adapter
$34.97
Ubiquiti Networks UniFi Security Gateway - White (USG-3P)
$49.00
OPNsense six-port Gigabit router/firewall on Lanner FW-7535 hardware
$69.00
$120.00
Fortinet FortiGate 60F | 10 Gbps Firewall Security Throughput (FG-60F)- Open Box
$381.99