The excellent Mike Martinez found this:
which works for many products. If it doesn’t find your part number and serial number, try the “HP Support Wizard”:
http://h50203.www5.hp.com/wclweb/wclentry.aspx
And if that doesn’t work, we have:
http://www8.hp.com/us/en/contact-hp/contact.html
As of this writing, there is a link on the far right of the above to a page entitled “HP Products”, subtitled “Live chat with HP support specialist”. On that page, enter the product name, not any number. Here is a direct link: