For readability, you normally use a monospaced font in the Terminal, and not regular fonts. DejaVu Sans Mono and Menlo support your sharp and flat characters, but you won't be able to enter them in the Terminal directly without using the character palette with a double-click on the character, or including the Unicode Hex Input method, added by System Preferences : Keyboard : Input Sources : [+] Others -> Unicode Hex Input. Also, [√] show input menu in menu bar.
In preparation to using Unicode Hex Input, visit System Preferences : Keyboard : Shortcuts : Input Sources, and choose [√] Select next source in input menu, and deselect Show Finder search window in the Spotlight shortcuts. Now, by pressing option+command+Spacebar, you can watch the input source icons change in the menu bar, and when you get to U+ which is the Unicode Hex Input, you can then press option key + unicode value to input the character. So for the music sharp character, it would be option+266f, and for the flat character, option+266d. When done, you cycle through option+command+Spacebar to get back to your preferred keyboard language.