i watched this yesterday - when bond takes the poison out (glass vile bit from inside the glass hexagon, ....the part with the fluid looks to be about approx 2.5-3 inches tall in scale) so too big for ballpoints imo
stab in the dark here - how about those cake decorating things - the metal tips for the icing bags
Tanks for the quick response guys. Yeah, I definitely will take a better look at the badger nozzle. So far it's the best candidate. Although I do not think the ballpoint tip is out of the question. If we say the glas vial is appr. 3in, then the tip would be appr. 7/8in. I measured a pen tip I had and it was 5/8in. I'm sure that if I find tips with the knurling at the bottom they will also be longer. I'm just thinking rational here. I mean if the pens exist it is not unlikely they used that solution. (think quantity, price)
Though the cake decoration nozzles look good, and are maybe close enough, they lack the knurling at the bottom plus they have a seam. I don't believe they were used. The part looks like it's in one piece and I'm almost certain that I've seen pen tips like that somewhere.
Below is a quick comparison of a screenshot and the pen tip I had. (the glove is just to match the scale better)
I was looking through the dump drawer in my kitchen I found this knife that reminded me of this thread. It's a helix retractable pen knife. It's got the knurling and looks to have the correct size hole in the end.
There are other airbrush brands that have similar nozzles, the Binks Wren and Paasche H were both available at the time. And the nozzles are sold separately as replacement parts, no need to buy a whole gun.