If you're looking for a way to retrieve everything around your where clause that would be rather difficult since there's no way to know where it would end. You could take a stab at grabbing a certain number of characters after the where clause but that would undoubtedly give you extra or not enough data
If you just want to know which stored procedures have where clauses you could do something like
select * from syscomments c
inner join sysobjects o on o.id = c.id
where c.text like '%where%' and o.type = 'p'
and then work through them.
that's off the top of my head so it may not be exact