you can try dictionary.columns, i.e.:
proc sql;
select name from dictionary.columns
where libname = upcase(your lib name) and memname eq upcase(your dataset name)
and name like "a%"
order by name;
quit;
/*
name: varialbe name
memname: dataset name
libname: library name
All libname and dataset name must be in uper case in the condition statament, no matter what they are in real situation.
*/