Well, if the National Two Spools (as I posted earlier) is not for you then there are the various vintage chain stitch machines which do not require a bobbin (like a Wilcox & Gibbs, Singer model 12 & various other vintage models) because they sew a chain stitch instead of a lock stitch.
Go here:
http://www.quiltingboard.com/vintage...t186496-5.html and check out the photos of the chain stitch made by my Wilcox & Gibbs.
There are other various vintage machines like the Singer 630 which has a 'spider' attachment. In a 'spider' install, you remove your bobbin, insert a round plate in the bobbin area, add an additional thread guide - the only thread used is thread from your spool which then creates a chain stitch.
Shari