I see... As far as I know, there is no function module, which would check AVC in this way. You should either develop your own reading FMAVCT table (and going through derivation strategy, if required) or use indirect way of checking out the availability: for example, for FI document, you can run BAPI_ACC_DOCUMENT_CHECK and see the outcome in the return messages. The issue is that AVC is checked by calling methods of class CL_FMAVC_LEDGER and not via function modules.
Function to read budget on budgetary address is not helpful. Because, budgetary address is not linked to AVC ledger and can be different from AVC control object. I'm afraid you have to write your own function, but it shouldn't be too complicated: you can simply call the class I gave you and use one of the available methods.