Sad news about Kenins' health.  The Centrediscs CD of his chamber music is
a fine one...

Holmboe's 2nd viola concerto certainly qualifies as "contemporary" (1991-2!)
Pettersson's viola concerto somewhat less so (1979, but then he died in 1980.)
(Glad to see Rubbra's wonderful one already mentioned ;)
Bacewicz' viola concerto is earlier (1968) but one of her last works
(she died, after all, in 1969.)
Gubaidulina's viola concerto dates from 1996.
Apparently (now from some web searching, anyhow...)
Sally Beamish (whose music has been surfacing on BIS lately) has a very
recent viola concerto;
so does Steven Gerber, whose music has been appearing on Chandos (his
dates from 1997).
Erland von Koch's 1940s viola concerto is hardly recent but has only
just gotten its world premiere recording, apparently...

Pehr Hendrik Nordgren's (1944-) 3 viola concerti (viola concerto #1,
1970, viola concerto #2, 1979, viola concerto #3, 1986).

-Eric Schissel (never a good violist and by now well out of practice...)