Do you own gear from defunct brands?

Yes. 
LSR&D mono SuperAmps refurbd and working

Original Genesis IM8300 3 way speakers

Some of my system is new, Sonus Faber Olympica Nova speakers, VPI Prime Signature turntable with VPI Shyla cartridge. I just replaced a twenty-year-old ARC PH-7 with a 15-year-old Pass Labs XP-25. Here's the kicker. I inherited a Hovland Radia Amp from an audiophile friend who passed away. Hovland has been out of business for over twenty years I think. The amp was raved about when it was new. It is a better amp than anything I could afford to replace it with. If anything like it exists. According to Bob Hovland, the designer and manufacturer, this amp was twenty years in the making. He'd only made tube amps prior to this one, and he wanted an amp with solid state punch and tube warmth. There isn't anything it doesn't do well, and I was lucky enough to have Bob Hovland check it over to make sure it was up to specs. There is so much about it I like, I don't plan on replacing it.

Literally all different... no two from the same manufacturer. Simaudio, Luxman, Micro-Seiki, AirTight, Audiomat, Lamm, Audio Note, Canor, Line Magnetic, Sonus Faber, Rogers, Altec, Lumin and even different cables & cords. Two systems at separate locations. Not sure why it unfolded this way but it's taken a long time putting these systems together and I'm super happy with both. 

Proceed amplifier (had two and went down to one after going stereo over multichannel). Lesser-known Madrigal Labs/Mark Levinson brand before they were taken over by Harman, and overbuilt like absolute tanks. Not everyone’s cup of tea appearance-wise, but internals are literally built to military specs and great solid-state AB sound. These things can push.

Very interesting list of posts. There are a few of my old favorites still floating around . Whether or not the company is still in business means nothing to me because I'm not living in the outback of Alaska. If I have a terrific McLaren preamp, I used to, from the late '80s and something just happens to go wrong with it, I'm surrounded by brilliant audio guys in the tri-state New York area who can solve the problem whether it be a capacitor or a volume control or whatever. There's nothing in the Holy Bible that says the manufacturer has to handle future issues.