I have available an archive of several hundreds of 1/4" data cartridges (typically 3M DC 600A 60MB 620ft/189m and equivalent), backups and Lisp sources. Standard format for Symbolics systems.

Original Zetalisp going back to Release 4? (1st after LM2), up to Release 8.3.
Most of Symbolics sys-op tools, low level disk build, IFS tape creation, S-Animation,
Nichimen 3D, Bones, Prolog, Boids, Kermit, Zeta-C,Plexi, Zippicalc, Fortran,
CLIM, CLOE, Joshua, KEE, ART, Statice, Pascal, Color, projects, ... you name
it, I may have it.
One cupboard:
A stack of 10 tapes weigh approx.: 2.83kg (6.3lb) and measure 162 x 117 x 226mm
(6.6 x 4.3 x 8.9 inches). So given up to. 500 tapes, I make that 140kg (312lb)
and 214 litres (i.e. 1/4 cubic meter, or 6.3 cu.ft.). Though to ship I think
some padding would be necessary to make the whole pack stronger.
Offers based on media costs (new were ~$25 each), say for $300 the lot.
Shipping your liability.
PS: FAQ answers: Almost all tapes are labelled. No I won't be making a list of the contents unless offered a financial incenive. And I have not counted the exact number of tapes. No I do not sell Symbolics software, suggest that you approach Symbolics for that.