M.2 SSD cards (QNAP QM2, Synology M2D/E10M20) and SAS / SATA expansion cards. Sorted by how many NAS models each is listed for.

PartNAS modelsBuy
QNAP QM2-2S-220A250Search Amazon eBay
QNAP QM2-2P2G2T229Amazon eBay
QNAP QM2-2P-244A225Amazon eBay
QNAP QM2-2P-384224Amazon eBay
QNAP QM2-2P-344221Amazon eBay
QNAP QXP-400eS-A1164200Search Amazon
QNAP QXP-800eS-A1164197Amazon
QNAP QM2-2P10G1TB196Amazon eBay
QNAP QXP-1600eS-A1164193Amazon
QNAP QM2-2P-344A186Amazon eBay
QNAP QM2-2S10G1TA186Amazon eBay
QNAP QM2-2P10G1T183Search Amazon eBay
QNAP QM2-2S10G1T183Search Amazon
QNAP QM2-2P-384A181Amazon eBay
QNAP QM2-2P10G1TA177Amazon eBay
QNAP QM2-2P167Amazon eBay
QNAP QM2-2S167Search Amazon eBay
QNAP QXP-1600eS158Amazon
QNAP SAS-12G2E141Amazon eBay
QNAP QM2-4S-240136Amazon eBay
QNAP QM2-4P-384134Amazon eBay
QNAP QXP-820S-B3408124Amazon eBay
QNAP QM2-4P-284109Amazon eBay
QNAP QXP-1620S-B3616W106Amazon
QNAP QM2-4P-34296Amazon
QNAP QXP-1630S-381653Search Amazon
QNAP QXP-830S-380853Search Amazon
QNAP SAS-6G2E-U44Amazon
Synology M2D2044Amazon eBay
QNAP QM2-2P410G1T42Amazon eBay
QNAP QM2-2P410G2T42Amazon
Synology M2D1828Amazon eBay
QNAP SAS-6G2E-D19Amazon
IEI Mustang-20011Search Amazon
Synology M2D178Amazon
QNAP QM2-2S10G1TB1Search Amazon