The Singer vintage machine site indicates that the AH251729 was made in 1947 in Elizabeth, NJ. For details see http://www.singermachines.co.uk/faq/tell-sewing-machine-age-from-two-letter-serial-number/
Look on the front of your sewing machine and locate the model number of the machine. Go to http://www.singerco.com/support/replacement-parts-chart
and locate your model number. (Use the drop down menu and locate the group. Press Go and then find the pdf with the correct model parts list.) You can look up the exact part number and order them from the Singer Service Center online.
Alternatively, you may be able to find them at any Singer Authorized retailer. Just look at your machine and determine the type of shank that connects foot to the machine. (High Shank and Slant are common Singer foot designs on older machines.) Get a zigzag foot for Singer machines with that design. (If they don't have that, you can probably get a current foot and an adapter. We got an overedge foot and the high slant foot adapter for my Singer sewing machine (purchased in 1969) in the 1980s.)
I hope this helps.
(Singer parts are generally available. I saw throat plates for some Featherweight machines this morning at a quilt show.)