We don’t have a product of an empty lens holder, but the existing lens assemblies do hold a standard 2 inch lens. The part, such as:
Replacement 20 cm Converging Lens for Optics Expansion Kit (L20B-OEK)

is intentionally designed to be hard to take apart (so students don’t do so). However, if you have other lenses that you want to use, you can always swap out the supplied lens with your own. The process takes a few minutes with a hex wrench. You would not want students doing it, and you would not want to make the swap frequently. But, if you want to use your own lenses, you can.

We don’t have these holders as separate parts, and getting a special order of just the plastic part would eat up the cost savings of not getting the lenses. You might just order one of the existing replacement lens with holder, and then swap in your own two inch lens.