North Country has been gone for around 20 years. The quartz parts can be made by TGP in Ohio.
https://technicalglass.com/about/
Windows and mirrors are available from Edmund Optics or Thor Labs.
https://www.thorlabs.com/navigation.cfm?guide_id=2264
It is important to note that the tubing parts must be quartz, not glass. Eagle Laboratory Glass can also make custom glass parts, and quartz on special request.
I wasted a lot of time on a voltage multiplier circuit to charge the cap. Now I am using a 15kv 30mA NST rectified which has proven to be rugged and reliable. If you are going to attempt this project, start shopping for your capacitor now. It was very difficult to find something suitable.
Last note, Light and its Uses suggests $100.00 project... Not even close. Assuming you already have some vacuum and high voltage equipment, plan on $1000.00 minimum to get started.
Hope this helps.
EDIT:
North Country's mirror were very old soft coated. The coating were actually water soluble. Modern dielectrics are much much better.