I thought I read that the factory that made parts for the older Berninas burned down and they were not being made now. I have an 830 Record that dates to 1972, but I haven't tried to buy anything for it for several years. My kids gave me the walking foot for Christmas one year, probably more than 10 years ago. I just noticed by looking on Sewing Parts Online, that the feet that work with the old 830 don't work with the 730, which I did not realize until now.
I have bought many parts for old machines from Sewing Parts Online and have had excellent success with compatibility. If they sell you something that didn't fit when they said it would, you could return it, I assume. Each part has a list of the brands and models that are compatible, so it's easy to verify before you buy.
Another option might possibly be a shank adapter that would allow you to attach low shank feet. A Bernina dealer, if they don't have the right walking foot, might have the shank adapter that would fit your machine, and they should know whether it would work with a low shank walking foot. I'd have them demonstrate this on your machine before you buy it because walking feet have bulky parts that might collide with an adapter. None of that would fit in with your quest to get the genuine parts, but if they're no longer being made, it might be the solution for making the machine do what you need it to do.