>Is there a utility within SQL Server or available as a third party product that can do 'code reference searches' for all stored procedures and functions within an instance of SQL Server?

Yes, there are third party utilities that can do this. I saw them referenced on Transact-SQL forum, will check later.

As a quick check, you can also do

select [Name], OBJECT_DEFINITION(object_ID) as [Code] from sys.procedures where OBJECT_DEFINITION(Object_ID) like '%SearchString%'

See also this relevant MSDN thread