I'm restoring a Gestetner 366 and always on the lookout for consumables and supplies: stencils, inks, screens, rollers, etc. Also, if you are keeping a Gestetner in operation and need help, let me know. I've learned a lot.
I know of no source for inks and stencils other than Ebay. A few years ago, I found plentiful supplies, but these have dried up over the past 2 years. I still see ink tubes sold, but almost no stencils. What a pity!