The lamp I'm using in real life works fine - I even get sharp shadows from objects both near and far from the projection screen. I don't know how to find its IES file, but it's a simple, small halogen light. I have imported the file from a light that looked similar, but to no avail.
I believe I would be helped by any solution that gives me sharp shadows in Lightup, even if the light source is different from what I use IRL. I think so, because I've replaced the light source before: the halogen lamp works, but so does the flashlight from my phone.