JAZZ Akiyoshi-Tabackin Big Band: ''Salted Ginko Nuts.'' Toshiko Akiyoshi, piano, conductor; Lew Tabackin, woodwinds; and the band. Ascent ASC. 10002. Wonderful! It's easy to understand why the Akiyoski-Tabackin Big Band has garnered top or close to top place in the jazz polls for the past five years. Although this album was recorded in Japan in 1978, this is its first American release. Akiyoshi originally formed the band ten years ago with one purpose - to perform her music. She writes all the material for the band, and with the help and support of her husband, Lew Tabackin, an outstanding jazz saxophonist and flutist, has brought her dream to fruition. On ''Salted Ginko Nuts,'' the astonishing talents of this couple have never been more evident. Toshiko's highly individual approach to writing - her beautifully harmonized five flutes on ''Elusive Dream,'' the human voicelike glissando passages behind Tabackin's brilliant solo on ''Chasing After Love,'' the unexpected twists and turns of melody and rhythm on ''Lazy Day'' - all of these demonstrate the scope of Akiyoshi's phenomenal talent. And the soloists! How rare it is to find consistently excellent improvisers in a band this size. Note especially the trombone battle on ''Salted Ginko Nuts,'' Dick Spencer's sassy alto solo on ''Son of Road Time,'' and Gary Foster's gorgeous alto on ''Elusive Dream.'' Highly recommended. This album is only available by mail order: Ascent Records, 38 West 94th Street, New York, N.Y. 10025. $8, plus $2 postage and handling, $4 for first class.