Where can I buy authentic JDM parts in the US?

Top US sources include JSpec Auto Sports, RHDJapan (ships internationally), Car Shop GLOW, and HKS USA for performance parts. For OEM JDM parts, Yahoo Japan Auctions via a proxy buyer (Buyee, FromJapan) is invaluable — you can find discontinued parts at reasonable prices. Domestic JDM forums (Skylines Australia, NASIOC, MR2OC) also have active classifieds with shipping to the US.