The only way to share 1 xducer to 2 units (besides Ethernet) is the discontinued HB US3 switch (unlikely you'll find one) ...
Humminbird Fishfinder Switch US3 | Free Shipping over $49!
There is no Y cable to split off 2d and send the 2d to another unit ...
Can you explain what or why you're trying to accomplish ...??
Rickie