Hi Sneha,
Thank you for the suggestion, but it's not quite what I'm looking for. I'm actually trying to be able to have the Product URL be visible on my quote mail merge document. I created a custom field for Opportunity Product that is called Opportunity Product URL on the Opportunity Product Form. What I think will work, but I can't solve the script, is to create a javascript that:
1) Set as On fieldChange of ExistingProduct
2) Find the ExistingProduct URL
3) Set the Opportunity Product URL to be this
However, this still only gets me halfway to my solution. It is not possible to map Opportunity Product fields to Quote Product fields, so even if I get the URL set correctly, I cannot pass it on later to the Quote. It is important for this, but also because we often add notes to specific products, and I'd like these notes, when entered for opportunity products to be visible/usable throughout the CRM process and on quotes.