From what I've gathered (and could be wrong) #5 is a Model C series machine.
I'm pretty sure this one takes the same needles and shuttle as the Singer - so very easy to find.
Feet are different - it takes the older style "Free" top clamp, so you have to watch for that. However they are not uncommon - just that most sellers don't have a clue what they have so they aren't listed as for the "free". And if they are, chances are it's the newer style and won't fit.
Free also "branded" machines, so there are a lot of models out there with other names on them.
When you look for attachments, look for a black metal box that says "attachments" on the front. There are ones out there with "Free" on them, but they are much less common.
Free takes a narrow gap foot - but specifically what you want to look for is the long plate with a circle cutout that is WIDE.
I'll post pictures - or you can PM me. I may have an extra set in my stash (I've got boxes of extras) and I can easily toss in a shuttle and some bobbins. This style is one I have lots and lots of extras.
If possible, please post a picture.