QNAP's USB and Thunderbolt network adapters. Sorted by how many NAS models each is listed for.

PartNAS modelsBuy
QNAP QNA-UC5G1T180Amazon eBay
QNAP QNA-UC10G1T11Amazon eBay
QNAP QNA-UC10G2SF11Search Amazon
QNAP QNA-UC10G2T11Search Amazon eBay
QNAP QNA-UC10G1SF10Search Amazon eBay
QNAP QNA-T310G1T7Amazon eBay
QNAP QNA-T310G1S - Thunderboltâ„¢ 33Amazon eBay
QNAP QNA-UC25G2SF1Search Amazon