Hey Candace,
Jenny (Sew-Classic) is advertising a walking foot specifically for the 301:
http://shop.sew-classic.com/Singer-S...A-SCF301WF.htm
It's labelled as an actual Singer part #. Her part number isn't a Singer part number though, and I think that's because it's "modified" per her description. If you look at both the one she lists for a 301, and the one she lists for "all other slants", you can see that what she's done is modify the original at the bar that goes above the needle clamp. Between the 2 listings, it's probably possible to figure out what to do to make it work properly. I have a Singer Slant walking foot here, I might see what I can figure out to make one work, just for the heck of it.
The walking foot that you linked to for the 15 and the 201 is "just" an Alphasew made walking foot. Any dealer can likely get it with that part number (P60400) and $20 is more than fair for it.