Here's the A's to get you started:
A., Jag - Abbatini, Antonio Maria - Abbiate, Louis - Abel, Carl Friedrich -bela, Placido Abelardo, Nicanor - Abert, Johann Joseph - Abing - Abril Tirado,Pedro - Abt, Franz - Accolay, Jean-Baptiste - Achron, Joseph - Adam, Adolphe - Adams, G - Adams, Mrs. Crosby - Adgate, Andrew - Adiego Navarro, Tomás - Adlgasser, Anton Cajetan - Adrianus, Gerard Nathanael - Adson, John - Afanasyev, Nikolay Yakovlevich - Agazzari, Agostino - Agnesi, Maria Teresa - Agnew, Roy -Agostini, Paolo -Agrell, Johan - Agricola, Alexander - Agricola, Martin - Aguado, Dionisio - Aguirre, Julian -Ahle, Johann Rudolf - Aichinger, Gregor - Aimon, Léopold -Aix, Pascal d' - Aizberg, Ilya - Akimenko, Theodore -Aksenov, Yegorov - Alain, Jehan - Alais, Juan - Alanus, Johannes - Alard, Jean Delphin - Alary, Georges -Alary, Giulio - Alassio, Serafino -Albéniz, Isaac -Alberdi, Juan Bautista - Albergati, Pirro Capacelli Conte - Albert, Eugen d' - Albert, Heinrich (d. 1651) -Albert, Heinrich (d. 1950) - Alberti, Domenico - Alberti, H. - Albinoni, Tomaso - Albrecht of Prussia, Prince Joachim - Albrecht, Ludwig Carl - Albrechtsberger, Johann Georg - Albrici, Vincenzo - Alcock Jr., John - Alcock Sr., John - Aldrovandini, Giuseppe Antonio Vincenzo - Alejandre Prada, Manuel -Alenev, Eugen Fedorovich - Aletter, Wilhelm - Alfano, Franco - Alferaki, Achilles - Aliani, Nicola - Alió, Francisco -Alkan, Charles-Valentin - Alkan, Maxime - Alkan, Napoléon - Allaga, Géza - Allegri, Gregorio - Allen, Euphemia - Allen, Paul Hastings - Allende, Pedro Humberto - Allier, Gabriel - Allison, Richard - Alnæs, Eyvind - Aloïz, Ladislas - Alpaerts, Flor - Alphonse, Maxime - Altès, Ernest Eugène - Altnikol, Johann Christoph - Alvarez, Fermin María - Alyabyev, Alexander - Amani, Nikolay - Amberg, Johan - D'Ambrosio, Alfredo - Ammon, Blasius - Amon, Johann Andreas - Anchorena, Emilio Vicente - Ancliffe, Charles - Andersen, Joachim - Andersen-Wingar, Alfred - Andersson, Richard - Andlauer, Louis Marie François - André, Johann - André, José - Andrée, Elfrida - Andrews, Ma - Anerio, Felice - Anfossi, Pasquale - Angeloni, Domenico - Angerer, Edmund - Anglebert, Jean-Henri d' - Anglia, Robertus de - Anglicanus - Ansorge, Conrad - Antalffy-Zsiross, Dezső - Antegnati, Costanzo - Antes, John - Antheil, George - Anthony, Bert R. - Antipov, Konstantin Afanasievich - Anton Sr., Philipp Gottlieb - Antonio, Lincoln - Antoniotto, Giorgio - Anzoletti, Marco - Aquabella, Ramon - Aranda, Omar - Arban, Jean-Baptiste - Arbeau, Thoinot - Arcadelt, Jacques - Arcas, Julián - Arditi, Luigi - Ardorino, Giovanni - Arena Rodríguez, Miguel Ramón - Arensky, Anton Stepanovich - Arifon, E.- Arimino, Ludvicus de - Ariosti, Attilio - Arndt, Felix - Arne, Thomas Augustine - Arnold, John - Arnold, Samuel - Arnoldi - Arntson, Steven - Arresti, Floriano - Arriaga, Juan Crisóstomo de - Arribas y Arribas, Juan - Arrieta, Emilio - Arrigo, Giuseppe - Arrigoni, Giovanni Giacomo - Artôt, Alexandre Joseph - Artsybushev, Nikolaï Vasilyevich - Artusini, Antonio - Asafiev, Boris Vladimirovich - Ascham, Roger - Ascher, Joseph - Ashton, Algernon - Asioli, Bonifazio - Asola, Giammateo - Asplmayr, Franz - Attaingnant, Pierre - Attrup, Karl - Attwood, Thomas - Auber, Daniel François Esprit - Aubert, Jacques - Aubert, V.B. - Audain, Irene - Audran, Edmond - Audsley, George Ashdown - Auer, Leopold - Aulen, Johannes - Aulin, Tor -Aulin, Valborg - Aurora.borealis - Austri, Giuseppe - Auzende, Ange-Marie - Avison, Charles - Avni, Boaz - Ayres, Frederick - Azanchevskiĭ, Mikhail Pavlovich
https://imslp.org/index.php?title=Category:Composers&from=A