I've found older equipment on ebay that I could never have found else
where. For example, here's an old Edison cylinder type record player:
http://tinyurl.com/64xjc Granted it isn't cheap but it is available and
within the financial reach of most people. My guess is you can buy just
about any outdated media-reading equipment you want on ebay. As for
reels of mainframe tape, I don't know of many people that have personal
data stored on them. I know the company I worked for had all those
tapes transfered to new media when they made the switch to PC's. I
suspect most people/companies did the same that had data they wanted to
access on newer systems.
Although we won't find tape readers etc. on the shelves of the local
electronics stores in the future there will likely be enough surviving
pieces of equipment to fill the demand for most needs.
As for LP's I never got into that media in a big way. I did have quite
a collection of cassettes but have found every old group I wanted
re-recorded on CD's. I have been steadily converting them to MP3 format
and have about 65 gigs of songs on the computer. It won't be long until
my whole collection of CD's is converted.
I do think that on-line storage is probably the best way to make sure
our personal information continues on after we're gone. That is until
the on-line storage company that stores the data goes out of business.