If you can't find a Bosch relay at your local auto store, you can order them online from www.partsexpress.com.
They have Bosch 30 amp SPDT listed in their printed catalog for $1.99!!
As John explained, the numbers I referred to are the terminal numbers for the relay. Here is a good reference on relay's:
Good luck with you project and let us all know how it turns out. Just remember to pay close attention to all connections. Use solder and heat shrink tubing for strong professional connections.