CRM Plug-in

I have a form in CRM called "Manual Purchase". By using a plug - in I want to retrieve the columns on that form and read the data out of that. Can someone tell me what kind of code I will need in order to retrieve the entity and then go through the controls of the entity.
I have attached a piece of code which does the same kind of stuff with "Opportunity" screen.
The problem I have is that I do not have somethng similiar to "TargetRetrieveOpportunity" for Manual Purchase,something like "TargetRetrieveManualPurchase" or similiar.

TargetRetrieveOpportunity target = new TargetRetrieveOpportunity();
                            target.EntityId = opportunityID;
                            RetrieveRequest retrieve = new RetrieveRequest();
                            retrieve.Target = target;
                            retrieve.ColumnSet = new AllColumns();
                            retrieve.ReturnDynamicEntities = true;
                            RetrieveResponse retrieved = (RetrieveResponse)service.Execute(retrieve);

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