Garmin HRM-DUAL Heart Rate Strap In-Depth Review | DC Rainmaker
Garmin HRM 3-SS will connect/pair with forerunner 35 but will not show heart rate (see picture) - Accessories & Sensors - Running/Multisport - Garmin Forums
AliExpress
Replacement Sensor module for Original Garmin HRM-RUN ANT+ Heart Rate Monitor 753759107741 | eBay