There is an ASN.1 encoder/decoder for Common LISP as part of a “SYSMAN” system, an SNMP implementation.  It doesn’t directly support CLISP :-(.  But the bits that seem troublesome are evidently pretty directed to SNMP MIBs…

I got something working via the combination of:

(dolist (file '("asn1-package" "dependent" "mib" "asn1-defs" "ber-defs" "ber-decode" "ber-encode"))
  (compile-file file)
  (load file))

Along with a few minor changes to some of the component files.  It looks like it works, but I haven’t really exercised it yet…