Recommendations for a bow to play a Violin Uke
Adventures with 'other' instruments...
A psaltery bow yes, would be ideal! It's more more nimble and light than even a short violin bow. The bow hair should be laid out in a small round 'rope' shape rather than a violin bow flat wide 'tape' shape...which I found gets caught on the zither pins too often when jumping quickly between the pins, as in bowed psatery playing.
In a pinch, for a rustic 'disposable' bow- you can even take an arched bent green branch between 1/4"-3/8" thick, cut deep notches at both ends, and set a hank of bow hair in it. Tie a knot at one end of the hair hank and lay it into one notch. Comb the hair straight without handling it in the middle (no finger grease!)...pull it to a good tension and lay it in the other notch by tying another knot at that end. Once you have it nicely set and tensioned to your liking, you can put a dot of glue on each knot to keep it in place well. Rosin it up very well to start with, then lightly thereafter.
You can buy black stallion horsehair hanks already measured and knotted at one end on Ebay, not that expensive. You can use a whole hank for a rustic bow, or half a hank if you want a thinner hair 'rope'. Some folks make a slight twist in the hair 'rope' when setting the hair in. I found that works well when making twisted horsehair strings, and personally I like non-twisted hair for bows.
I've found that such rustic 'bent stick/hank of hair' bows work surprisingly well and are kind of fun for psalteries, rebecs, jouhikkos, etc. If you use an underhand grip to bow (as with a jouhikko/tagelharpa) you can leave the hair more slack because you tension the hair while playing, with your bow grip hand.