A list of recommended compositions and links where you can buy the scores

Violin
1/ F. Ondříček: Scherzo Capriccioso for Violin and Piano Op. 18 
2/ B. Martinů: Five Madrigal Stanzas H.297 (1943) - selection
3/ B. Martinů: Sonate for Violin and Piano nu. 2 H.208 (1931) – (I. Allegro moderato, III. Poco Allegretto)
4/ S. Bodorová: „Dža more“ for violin solo

Cello
1/ A. Dvořák: Silent Woods, Op. 68
2/ J. Suk: Ballade and Serenade, Op. 3
3/ B. Martinů: Variations on a Theme of Rossini
4/ B. Martinů: Variations on a Slovakian Theme

Piano
1/ B. Martinů: Three Czech Dances (Dupák)
2/ V. Novák: Reminiscences Op. 6 (Inquieto)
3/ A. Dvořák: Humoresques Op. 101(one of following: nu. 1, nu. 5, nu. 8.) 
4/ V. Kalabis: Accents Op. 26 (selection)
5/ J. Gemrot: Short Story for Piano

Guitar
1/ Š. Rak: Suite of the Renaissance (6. Temptation of the Renaissance) 
2/ L. Sommer: Canzona e toccata per chitarra
3/ M. Zelenka: Unfinished Variations on the Theme of Jana Obrovská

Cembalo
1/ V. Kalabis: Akvarely (1st part) 
2/ J. Teml: Diptych for Harpsichord (1st part, Fantasia)
3/ J. Novák: Sonata brevis 
4/ B. Martinů: Deux pièces
5/ B. Martinů: Sonate

Harp 
1/ J. K. Krumpholtz: Preludium nu. 1, Op. 2 
2/ J. Pauer: Partita (Intermezzo + Toccatina)
3/ M. Kymlička: Simple music for Harp
4/ I. Hurník: Dances for Harp

Accordion
1/ E. Douša: Pocta mistrům
2/ J. Feld: Dvojhlasá partita; Petite prelude
3/ P. Fiala: Nálady; Sonatina brevis
4/ O. Kvěch: Snapshots
5/ J. Matys: Bagatelles
6/ J. Teml: Miniatures
7/ P. Trojan: Small suite for accordion; Days
8/ J. Truhlář: Suite for Ivo

Flute
1/ B. Martinů: Scherzo 
2/ O. Kvěch: 6 Preludes (I. Melodia semplice, II. Scherzino, III. Rubato)
3/ J. Mysliveček: J. Mysliveček: Flute Concerto in D major - 1st movement 
4/ V. Blodek: Andante cantabile

Clarinet
1/ E. Douša: Rhapsody for Clarinet a Piano
2/ Z. Matějů: Smorfia for Clarinet and Piano 
3/ B. Martinů: Clarinet Sonatina (1st movement)
4/ V. Černohorská: Rondo for Clarinet and Piano

Bassoon
1/ P. Čotek: Prelude et theme varié for Bassoon and Piano 
2/ E. Hlobil: Divertimento for Bassoon and Piano 
3/ O. Mácha: Sonate for Bassoon and Piano - 2nd movement 
4/ K. Sodomka: Andantino and Scherzando for Bassoon and Piano
5/ A. Rejcha: Variations for Bassoon and String Quartet (adjusted for bassoon and paino)

Trumpet
1/ B. Martinů: Sonatine for Trumpet and Piano
2/ J. Filas: Sweet bitternesses

Oboe
1/ L. Sommer: Small Sonata for Oboe and Piano
2/ O. Flosman: Sonatina for Oboe and Piano
3/ P. Eben: Sonata for Oboe and piano - 1st and 2nd movements

French Horn
1/ J. D. Škroup: Concerto for French Horn in B flat Major
2/ J. Kofroň: Sonatina for French Horn and Piano - 2nd and 3rd movements 

Trombone
1 / L. Simon: Fantasy for Trombone and Piano
2/ V. Smita: Romance for Trombone and Piano
3/ J. Dvořáček: Inventions for Trombone and Piano
4/ O. Blaha: Suita for Trombone and Piano
5/ I. Loudová: Ballata antica for Trombone and piano