Most things have the ability to have two drops down which could be used to allow a person to select CL and Spell Level.
Assuming you have the community Pack installed you can use the following custom expressions to produce a pair of dropdowns:
Use this for a selection of spell levels 0-9
Code:
component.SelectHelp & PackSelect.SpellLevel
Use this for a selection of caster levels 1-20
Code:
component.SelectHelp & PackSelect.CharLevel
Then you can test the tag "Value.?" to for each chooser to figure out the spell/caster level chosen.