How can I use a string argument to case a namespace or type?

I need to get some JSON output in a .NET 2.0 C# script. The goal is to use one method to output all the JSON feeds I need. All the models have the same id and name properties so I have about 15 namespaces that have the same parts here. In short: since I'm use castle I can call the function like:

/public/get_place_tags.castle
/public/get_place_types.castle
/public/get_place_whichEver.castle

Which in castle is calling each method, ie: the get_place_tags(){} but I want to not have to work where I can call one method to get output from each type like this:

/public/get_json.castle?wantedtype=place_types

Does anyone know how to fix this?

namespace campusMap.Controllers
{
    [Layout("home")]
    public class PublicController : BaseController
    {
        /*  works and returns */
        public void get_pace_type()
        {
            CancelView();
            CancelLayout();

            place_types[] types = ActiveRecordBase<place_types>.FindAll();
            List<JsonAutoComplete> type_list = new List<JsonAutoComplete>();

            foreach (place_types place_type in types)
            {
                JsonAutoComplete obj = new JsonAutoComplete();

                obj.id = place_type.place_type_id;
                obj.label = place_type.name;
                obj.value = place_type.name;

                type_list.Add(obj);
            }

            string json = JsonConvert.SerializeObject(type_list);
            RenderText(json);
        }

        /*  can;t ever find the namespace */
        public void get_json(string wantedtype)
        {
            CancelView();
            CancelLayout();
            Type t = Type.GetType(wantedtype); 

            t[] all_tag = ActiveRecordBase<t>.FindAll();
            List<JsonAutoComplete> tag_list = new List<JsonAutoComplete>();

            foreach (t tag in all_tag)
            {