Hi!
Firstly you can find family symbols with specific parameter values, using .WhereElementIsElementType() method combined with parameters filter(s), search "ElementParameterFilter" in chm file from Revit SDK and ElementCategoryFilter.
Then use FamilyInstanceFilter to find family instances of specific family symbols you've founded earlier.
The largest collection of filtering samples can probably be found in The Building Coder samples module CmdCollectorPerformance.cs:
All samples presented there are discussed and explained in some blog post or other.
Cheers,
Jeremy