How to manually issue an invoice or how to enable a product to a specific customer?

Hi,
The product I sell in my store is Stone Guitar Picks where each pick is unique, hence “Max Quantity” field is always set to 1.
However I also offer wholesale prices in which case the purchase is not done through the shop but rather by me sending
A PayPal request for payment.
The thing is I am often being asked for a store invoice and my question (actually two) are:

1. Does ZenCart give a way to issue an invoice manually?
2. Alternatively I could make up a special product tailored for a specific product/quantity/customer and add it to the store and instruct the customer to purchase that item but in this case I need the ability of ZenCart to somehow “hide” this product from any other customers so no one purchases it accidently. (very much in the same way eBay does)
   Any help on the matter is very much appreciated.
   Thanks,
   Amnon