Hello & Welcome to Just Answer,
Sorry to hear of any issue using your device.
I believe what you are referring to is the "USB ANT Stick" - that allows you to connect to the computer. And yes, these ARE available as a separate item in a couple of different places.
First, I have a link to the Garmin page where these are sold - for FULL price (~$50).
Click Here for Garmin Listing --> https://buy.garmin.com/en-US/US/shop-by-accessories/fitness-sensors/usb-ant-stick-/prod10997_010-01058-00.html
BUT, you can also get them on Amazon, for less than half the cost shown on the Garmin page. Click link below to see that listing.
Click Here for Amazon Listing --> http://amzn.to/2bSlF8t
Please let me know what you find or if you have any more questions.
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Thanks, ***** *****