Unicode Hex Input
You can use Unicode Hex Input to enter the characters that you want. Go to System Preferences → Keyboard → Input Sources and enable Unicode Hex Input. Then you can enter the characters by holding ⌥ and typing the Unicode code.
Multi-stroke Key Bindings
You can edit ~/Library/KeyBindings/DefaultKeyBinding.dict and create a multi-stroke key binding for each of the characters that you want to enter. More information is available on this blog post:
Press and Hold
Append the following to the
Keyboard-en.plist file (before the closing
There are a number of different spaces included in the strings above.
Feel free to change the
Roman-Accent-t to any character you wish, providing it does not already have Press & Hold keys assigned.
Go to System Preferences → Keyboard → Text and enter some shortcuts.