Where to find white ink for letting/naming my bow?

Yep. Craft stores (Hobby Lobby, Michaels, Dick Blick, etc.)  I use India ink with a metal nib pen.

never had good luck with india ink or a pen.  not sure why.

With India ink you have to really mix it up well each time, especially the first time.  Otherwise it will have a watery consistency. Perhaps that was the trouble?

I've just tried a normal dipping pen (quill) and instead of ink (which doesn't seem to stick well to the glass) I used normal white acrylic paint. the water based kind sold in cheap sets of model paint. Worked absolutely brilliantly    You just have to add a little water to get the consistency to the point where you can write with it using the pen.
Bonus part is the paint cost less than a 10th what a bottle of ink would have cost.