Note.....Renkus SSD-1800 diaphragms are no longer made, but if your quick.....
I think i still have one NOS phragm left somewhere, i bought 4 about 10 years ago from a mastering studio not too far from here that was also a parts supplier for the microphone and speaker repair industry. I've never needed a replacement, so ebay'd the others off here and there for "play" money. I've never really counted, but i probably have ~50 working Altec/Emilar/Renkus small format drivers floating around here. I've got spares to last the rest of my lifetime, or for as long as i can still hear, whichever comes first.

FWIW, a few years back a gentleman(who's name escapes me, apologies) posted here or maybe at AK or both who had worked with Jonas Renkus. I think our friend Steve Schell can fill in the blanks where my memory fails, as i believe this gentleman was staying with Steve at or around the time of his posting. he gave some great insight into the diaphragm construction, i think he helped Renkus develop the "tri-laminate" material that the phragms are constructed from.

Maybe some of the old posts have survived the various server migrations, i'll do some searching and see what i can find.