Singer 12 or New family needles, shuttles, and feet are available on ebay, though costly. 3 needles go for $12-$16. Shuttles and attachments would be tougher to find but not impossible. Millions of these were made. I had a treadle 12 and am not a fan personally but I suppose it was a wonderful improvement in its day. A hand crank might be nicer.
The 319 uses 206x13 needles which are available from sew classic for $8 for 10 needles. I hear mixed reviews but have never used one.
Ismacs should have manuals on both.
Jon