I'm getting into repairing electronics and would like to be able to look closer at failing components. The Zink Selenide lenses, that are being sold, are insanely overpriced. I can't find the focal length and diameter required for the lens, so I can order just the lens cheap.
You need a ZnSe convex or planoconvex lens. Placing it in front of your existing lens will allow it to focus closer.
Search for "ZnSe lens" on your favorite shopping sites. Many are listed as condenser lenses for CO2 lasers for around $15-20.
Make sure the diameter is large enough to cover the front element of your existing lens. Thare aren't really any other relevant specs since you'd be using it as an auxiliary lens to modify the function of your existing lens.
See YouTube: DIY Macro Mode for a Seek Thermal Camera