Laura,
In my experience the Singer treadles seem to be the easiest to find parts for. I have 2 Singer treadles, a 201K and 15-90(did a motorectomy), they both use common low
shank feet and modern needles.
You can also treadle some of the Japanese 15 clones, just do a motorectomy; plus they come in really pretty colors and will fit into a Singer treadle cabinet.
The first machine is a Singer 201k and the other is a Singer 15-90
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