Complex form issue

I'm designing an application that has products and suppliers. Single
product has_many suppliers and each supplier has unique supplier code
for each product.

The form would facilitate something like
1. Select supplier from the list --> 2. Type the supplier code related
to supplier in the text field

The supplier codes can be added dynamically.

#Product model
class Product < ActiveRecord::Base
  has_many :supplier_codes
  has_many :suppliers, :through => :supplier_codes
end

#Supplier_code model
class SupplierCode < ActiveRecord::Base
   belongs_to :product
   belongs_to :suppliers
end

#Supplier model
class Supplier < ActiveRecord::Base
   has_many :supplier_codes
   has_many :products, :through => :supplier_codes
end

The supplier_code table has these columns
product_id
supplier_id
code

I'm stuck with developing controller and form. trying out many things
but no success so far. Any help welcome.