These connectors are a bear to make yourself, so this cable takes the pain and suffering out of the process and let's you get right to communicating to your GPS.
Garmin part number 325-00026-00
The price for the Garmin GPS-20/GPS-25 Data Cable is:
$ 15 US for members of TAPR
$ 15 US for non-members+ shipping/handling if applicable.
Shipping and Handling
Shipping and Handling within the US will be by USPS Priority Mail.
International shipping costs are calculated as closely as possible. If the actual cost exceeds the estimate by more than $5.00, TAPR will contact you to get approval for the additional funds. TAPR uses insured Priority Mail International, unless the purchaser requires something else.