Some works by Rudolf Karel have been recorded (I don't believe I've heard
any.) On LP:  his Revolucni prehedra (op.  39) was on Panton LP 11 0360 (ca
1972), Czech Phil.  cond.  Smetacek with works by Burian, Pauer and Nejedl.

On CD:
his nonet for woodwind, horn and strings, op.  43 on Koch Schwann 3-1371-2
(ca 1994) played by members of the Bayerische Kammerphilharmonie, cond.
Yinon (I think), with works by Haas, Klein and Schulhoff.

Another recording of the nonet on Ars Musici AM 1234-2 (ca 1999) (Ensemble
aventure, cond.  Hommel) with works by Erich Itor Kahn and Hans Krasa.

Yet another recording of the nonet (!!) on Supraphon SU 3339-2 131 (ca
1997), with works by Haas, Klein, and Luck; Academia Wind Quintet Prague
and members of the Panocha Quartet.

On Supraphon SU 3266-2 (ca 1997, some performances from 1954), scenes from
the operas Death grandmother and Three Hairs of the Wise Old Man (many
performers...)

His theme and variations for piano op.  13 are on Arion CD ARN 68339 with
works by Haas, Klein,and Ullmann (Suite, Sonata and Sonata 6; played by
Francesco Lotoro; released ca.  1995.)

Partial list, anyhow... hope that's of some value.

-Eric Schissel