Shimano Part Number: Y012AN842. Bladed silver straight pull spoke with 14g thread. Shipping Weight: 10g.
This spoke is our recommended substitute for Shimano Part Number Y4BE98040 (Front spoke for WH-R550, no longer available). This spoke is 2mm shorter and lacks the thick rim washer (you'll need to reuse your old one: Good Luck!). We've not done this ourselves but seems the most likely to work.