Not sure if this will help or not, but IBTanked sells custom sized glass on their site. All you do is give them the measurements.
I've not done this, but I haven't seen many other places that do this. You can find the owner (?) on this forum. Goes by OCD.
But as mentioned above a plastic syringe may be a great temporary fix. Maybe thicker or thinner o-rings on it if it doesn't fit perfectly.