You will need to buy a deed/chasis blueprints from a Shipwright. To find their vendors, access a bazaar and then select "Vendor Locations". Then you will have to select either "Planet" or "Entire Galaxy" search, which is on the left side of the bazaar screen. Then, make sure you click on "All" under the items tab, then enter the text "Y-wing" in proper spot and hit enter. You should then get a few if not tons of choices of Y-wings, pick the location you prefer and select "Create Waypoint"...just make sure you select the right Y-wing, there is also a Y-wing Longprobe and I don't remember which one you get license for first, just make sure...
Sorry that was so wordy

feel free to ask for any clarification...and if you are on Starsider, feel free to look up my shipwright.