Joe,

Sounds like your 3 year old had the most fun <img src="http://www.catsailor.com/forums/images/graemlins/laugh.gif" alt="" />.
Also sounds like the gooseneck travels on a sliding track. Is that correct ? <img src="http://www.catsailor.com/forums/images/graemlins/ooo.gif" alt="" /> Haven't seen that setup since my days of sailing scow Moths. Most of the Mozzies have a fixed gooseneck position and adjust the downhaul constantly with a pulley system for sail flatness/fullness. See link to image below.
http://s51.photobucket.com/albums/f392/v...gAnch=imgAnch17
The gooseneck fitting is rivetted to the mast and your 3 year old will never be able to remove it <img src="http://www.catsailor.com/forums/images/graemlins/cool.gif" alt="" />

If you really want to just replace the missing part and don't think that it's a Rostan Fitting then try making an enquiry with Riley via the link below:

http://www.rileyfittings.com/index.html

If you think that the gooseneck system replacement is justified then Australian High Performance Catamarans (AHPC) can mail orders anywhere. The gooseneck system in the image is from AHPC. http://www.ahpc.com.au/home.htm Just mention that it is for a Mozzie and it should be easy to fit assuming that you have a rivetting gun. I phoned AHPC for a hound fitting on Wednesday and had the part delivered on Friday.

Regards,

Peter <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />

I've given the product number from Riley in my earlier post, I don't think you'll be able to order the fitting direct, and website is not much good for gaining specific information. The catalogue I am refering to is the latest.
Peter is right though, if you want a more modern, fixed fitting the AHPC gooseneck would be the way to go, you would looking at $75.00 for a AHPC gooseneck, I don't know what your replacement Riley fitting would be.

Regards